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Postretirement Benefit Plans - Company's Asset Allocations for its U.S. Pension Plans by Asset Category (Detail) - United States [Member] - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | $ 175,336 | $ 160,423 | $ 134,198
Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 124,106 | 115,591 |
Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 51,230 | 44,832 |
Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 7,056 | 7,261 |
Cash and Cash Equivalents [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 7,056 | 7,261 |
Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 105,898 | 97,250 |
Equity Securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 105,898 | 97,250 |
U.S. Equities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 54,805 | 50,319 |
U.S. Equities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 54,805 | 50,319 |
Non-U.S. Equities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 23,155 | 19,697 |
Non-U.S. Equities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 23,155 | 19,697 |
Employer Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 27,938 | 27,234 |
Employer Securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 27,938 | 27,234 |
Fixed Income Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 62,382 | 55,912 |
Fixed Income Securities [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 11,152 | 11,080 |
Fixed Income Securities [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 51,230 | 44,832 |
U.S. Corporate Bonds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 41,489 | 36,242 |
U.S. Corporate Bonds [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 41,489 | 36,242 |
U.S. Government and Agency Bonds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 12,722 | 11,080 |
U.S. Government and Agency Bonds [Member] | Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 11,152 | 11,080 |
U.S. Government and Agency Bonds [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 1,570 |  |
Other Bonds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 8,171 | 8,590 |
Other Bonds [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | $ 8,171 | $ 8,590 |

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