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Pension Plans and Postretirement Benefits - Summary of Total Investments Measured at Fair Value (Detail) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | $ 921,307 | $ 1,310,311 |
Unclassified | 537,569 | 655,149 |
U.S. Government Securities |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 305,995 | 369,980 |
Unclassified | 0 | 0 |
Commingled and Mutual Funds |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 230,674 | 358,423 |
Unclassified | 188,494 | 280,743 |
Real Estate |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 132,867 | 126,886 |
Unclassified | 132,867 | 126,886 |
Diversified Credit |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 108,363 | 133,508 |
Unclassified | 108,363 | 133,508 |
Fixed Income |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 95,967 | 182,169 |
Unclassified | 60,404 | 21,484 |
Partnerships with Security Holdings |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 25,259 | 46,515 |
Unclassified | 25,259 | 46,515 |
Cash, Cash Equivalents and Accrued Items (1) |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 22,182 | 46,013 |
Unclassified | 22,182 | 46,013 |
Investment Contracts |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets |  | 46,817 |
Unclassified |  | 0 |
Level 1 |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 383,738 | 474,831 |
Level 1 | U.S. Government Securities |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 305,995 | 365,295 |
Level 1 | Commingled and Mutual Funds |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 42,180 | 77,680 |
Level 1 | Real Estate |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 1 | Diversified Credit |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 1 | Fixed Income |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 35,563 | 31,856 |
Level 1 | Partnerships with Security Holdings |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 1 | Cash, Cash Equivalents and Accrued Items (1) |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 1 | Investment Contracts |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets |  | 0 |
Level 2 |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 133,514 |
Level 2 | U.S. Government Securities |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 4,685 |
Level 2 | Commingled and Mutual Funds |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 2 | Real Estate |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 2 | Diversified Credit |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 2 | Fixed Income |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 128,829 |
Level 2 | Partnerships with Security Holdings |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 2 | Cash, Cash Equivalents and Accrued Items (1) |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 2 | Investment Contracts |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets |  | 0 |
Level 3 |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 46,817 | $ 0
Level 3 | U.S. Government Securities |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 3 | Commingled and Mutual Funds |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 3 | Real Estate |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 3 | Diversified Credit |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 3 | Fixed Income |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 3 | Partnerships with Security Holdings |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | 0 | 0 |
Level 3 | Cash, Cash Equivalents and Accrued Items (1) |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets | $ 0 | 0 |
Level 3 | Investment Contracts |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |
Total Assets |  | $ 46,817 |

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