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Employee Benefit Plans - Plan Assets Measured and Reported in Financial Statements at Fair Value (Detail) - Defined benefit pension plans - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 457,880 | $ 431,747 | $ 401,929
Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 323 | 618 |
Level 1 | U.S. government and U.S. government agency securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 1 | U.S. corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 1 | International corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 1 | Mutual funds (a) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 1 | Money market funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 323 | 618 |
Level 1 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 1 | Insurance "buy-in" policy |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 109,779 | 102,905 |
Level 2 | U.S. government and U.S. government agency securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 14,132 | 16,196 |
Level 2 | U.S. corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 69,708 | 57,669 |
Level 2 | International corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17,490 | 14,088 |
Level 2 | Mutual funds (a) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 2 | Money market funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 2 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 8,449 | 14,952 |
Level 2 | Insurance "buy-in" policy |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 32,794 | 31,281 |
Level 3 | U.S. government and U.S. government agency securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 | U.S. corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 | International corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 | Mutual funds (a) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 | Money market funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
Level 3 | Insurance "buy-in" policy |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 32,794 | 31,281 |
Fair Value, Inputs, Level 1, 2 and 3 | U.S. government and U.S. government agency securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 14,132 | 16,196 |
Fair Value, Inputs, Level 1, 2 and 3 | U.S. corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 69,708 | 57,669 |
Fair Value, Inputs, Level 1, 2 and 3 | International corporate debt instruments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17,490 | 14,088 |
Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds (a) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 73,314 | 74,750 |
Fair Value, Inputs, Level 1, 2 and 3 | Money market funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 323 | 618 |
Fair Value, Inputs, Level 1, 2 and 3 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 8,449 | 14,952 |
Fair Value, Inputs, Level 1, 2 and 3 | Insurance "buy-in" policy |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 32,794 | 31,281 |
Fair Value Measured at Net Asset Value Per Share | Collective trust funds, U.S. equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 86,175 | 78,170 |
Fair Value Measured at Net Asset Value Per Share | Collective trust funds, International equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 94,812 | 89,381 |
Fair Value Measured at Net Asset Value Per Share | Collective trust funds, International fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17,799 | 15,387 |
Fair Value Measured at Net Asset Value Per Share | Collective trust funds, diversified funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 42,884 | $ 39,255 |

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