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Pension Plans - Projected Benefit Obligation and Fair Value of Plan Assets (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Funded Status Of Plan [Abstract]      
Projected benefit obligation at beginning of the year $ 37,936 $ 33,931  
Service cost 0 299 $ 250
Interest cost 1,301 1,411 1,349
Actuarial loss (gain) 4,590 3,528  
Benefits paid (1,245) (1,233)  
Projected benefit obligation at end of year 42,582 37,936 33,931
Fair value of plan assets at beginning of the year 32,658 28,672  
Actual return on plan assets 5,013 5,219  
Employer contributions 330 0  
Benefits paid (1,245) (1,233)  
Fair value of plan assets at end of the year 36,756 32,658 $ 28,672
Unfunded pension obligation $ 5,826 $ 5,278