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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