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Pension Plans and Other Postretirement Benefit Plans - Schedule of Fair Value Hierarchy of pension Plan's Assets (Details) - Pension Plan And SERP [Member] - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 722,024 | $ 642,063 | $ 544,051
Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,309 | 2,852 |
Fixed Income Securities [Member] | US Government Debt Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 10,990 | 37,297 |
Fixed Income Securities [Member] | Domestic Corporate Debt Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 279,857 | 207,222 |
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 39,634 | 35,836 |
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 22,431 | 23,539 |
Mutual Funds [Member] | U.S Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 146,375 | 173,568 |
Mutual Funds [Member] | International Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 96,311 | 46,416 |
Mutual Funds [Member] | Absolute Return [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 11,640 | 16,720 |
Common/Collective Trusts [Member] | Real Estate [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 29,532 | 31,473 |
Partnership And Closely Held Investments [Member] | International Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 26,760 |  |
Partnership And Closely Held Investments [Member] | Absolute Return [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 47,188 | 59,260 |
Partnership And Closely Held Investments [Member] | Real Estate [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 7,997 | 7,880 |
Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 254,326 | 236,704 |
Level 1 [Member] | Mutual Funds [Member] | U.S Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 146,375 | 173,568 |
Level 1 [Member] | Mutual Funds [Member] | International Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 96,311 | 46,416 |
Level 1 [Member] | Mutual Funds [Member] | Absolute Return [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 11,640 | 16,720 |
Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 356,221 | 306,746 |
Level 2 [Member] | Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,309 | 2,852 |
Level 2 [Member] | Fixed Income Securities [Member] | US Government Debt Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 10,990 | 37,297 |
Level 2 [Member] | Fixed Income Securities [Member] | Domestic Corporate Debt Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 279,857 | 207,222 |
Level 2 [Member] | Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 39,634 | 35,836 |
Level 2 [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 22,431 | $ 23,539 |

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