Pension and other postretirement benefits - Fair values of pension plan assets (Detail) - USD ($) $ in Thousands | 12 Months Ended | |
Dec. 31, 2021 | Dec. 31, 2020 |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Maximum percentage of net assets invested in emerging market | 35.00% | |
Minimum | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Effective average duration to maintain | 3 years | |
Maximum | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Effective average duration to maintain | 10 years | |
Emerging markets debt fund | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Percentage of net assets invested in foreign equity securities | 80.00% | |
Small and Mid-Sized Companies | Equity Securities | U.S. Russell 2500 Index | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Percentage of net assets invested | 80.00% | |
Foreign Companies | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Percentage of net assets invested in foreign equity securities | 80.00% | |
Fair Value, Measurements, Recurring | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | $ 469,793 | $ 457,626 |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 459,105 | 429,882 |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 439,093 | 414,299 |
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 879 | 5,094 |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 19,133 | 10,489 |
Fair Value, Measurements, Recurring | Fair Value Measured at Net Asset Value Per Share | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 10,688 | 27,744 |
Fair Value, Measurements, Recurring | Cash | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 923 | 582 |
Fair Value, Measurements, Recurring | Cash | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 923 | 582 |
Fair Value, Measurements, Recurring | Cash | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Cash | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Money market funds | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 6 | 12 |
Fair Value, Measurements, Recurring | Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 6 | 12 |
Fair Value, Measurements, Recurring | Money market funds | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Money market funds | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Managed Volatility | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 57,252 | 85,974 |
Fair Value, Measurements, Recurring | Managed Volatility | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 57,252 | 85,974 |
Fair Value, Measurements, Recurring | Managed Volatility | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Managed Volatility | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | U.S. Small/Mid-Cap Equity | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 7,532 | 11,780 |
Fair Value, Measurements, Recurring | U.S. Small/Mid-Cap Equity | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 7,532 | 11,780 |
Fair Value, Measurements, Recurring | U.S. Small/Mid-Cap Equity | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | U.S. Small/Mid-Cap Equity | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | World equity (excluding U.S.) | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 34,287 | 59,467 |
Fair Value, Measurements, Recurring | World equity (excluding U.S.) | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 34,287 | 59,467 |
Fair Value, Measurements, Recurring | World equity (excluding U.S.) | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | World equity (excluding U.S.) | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Intermediate duration bond fund | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 101,363 | 63,376 |
Fair Value, Measurements, Recurring | Intermediate duration bond fund | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 101,363 | 63,376 |
Fair Value, Measurements, Recurring | Intermediate duration bond fund | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Intermediate duration bond fund | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Long duration bond fund | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 171,919 | 98,996 |
Fair Value, Measurements, Recurring | Long duration bond fund | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 171,919 | 98,996 |
Fair Value, Measurements, Recurring | Long duration bond fund | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Long duration bond fund | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate bond fund | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 7,607 | 13,469 |
Fair Value, Measurements, Recurring | Corporate bond fund | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 7,607 | 13,469 |
Fair Value, Measurements, Recurring | Corporate bond fund | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate bond fund | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Emerging markets debt fund | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 7,605 | 11,412 |
Fair Value, Measurements, Recurring | Emerging markets debt fund | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 7,605 | 11,412 |
Fair Value, Measurements, Recurring | Emerging markets debt fund | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Emerging markets debt fund | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate, government and foreign bonds | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 50,599 | 35,582 |
Fair Value, Measurements, Recurring | Corporate, government and foreign bonds | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 50,599 | 35,582 |
Fair Value, Measurements, Recurring | Corporate, government and foreign bonds | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate, government and foreign bonds | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Absolute return credit fund | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 671 | |
Fair Value, Measurements, Recurring | Absolute return credit fund | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | |
Fair Value, Measurements, Recurring | Absolute return credit fund | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 671 | |
Fair Value, Measurements, Recurring | Absolute return credit fund | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | |
Fair Value, Measurements, Recurring | Asset backed – home loans | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 208 | 261 |
Fair Value, Measurements, Recurring | Asset backed – home loans | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Asset backed – home loans | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 208 | 261 |
Fair Value, Measurements, Recurring | Asset backed – home loans | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Contract with insurance company | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 19,130 | 10,485 |
Fair Value, Measurements, Recurring | Contract with insurance company | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Contract with insurance company | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Contract with insurance company | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 19,130 | 10,485 |
Fair Value, Measurements, Recurring | Other | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 3 | 4 |
Fair Value, Measurements, Recurring | Other | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Other | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Other | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | $ 3 | 4 |
Fair Value, Measurements, Recurring | Common equity securities | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 29,592 |
Fair Value, Measurements, Recurring | Common equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 29,592 |
Fair Value, Measurements, Recurring | Common equity securities | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 0 |
Fair Value, Measurements, Recurring | Common equity securities | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 0 |
Fair Value, Measurements, Recurring | Multi asset funds | Fair Value, Inputs, Level 1, 2 and 3 | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 8,890 |
Fair Value, Measurements, Recurring | Multi asset funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 4,057 |
Fair Value, Measurements, Recurring | Multi asset funds | Significant Observable Inputs (Level 2) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | 4,833 |
Fair Value, Measurements, Recurring | Multi asset funds | Significant Unobservable Inputs (Level 3) | | |
Schedule Of Pension Plan Assets By Fair Value [Line Items] | | |
Fair value of plan assets | | $ 0 |