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Employee Deferred Compensation Plan and Employee Stock Purchase Plan - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 12 Months Ended
Jun. 30, 2001
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Nov. 05, 2018
Jun. 06, 2018
Employee Stock Ownership Plan E S O P Disclosures [Line Items]            
Percentage contribution, compensation   100.00%        
Matching percentage, employee contribution   5.00%        
Company's contributions amount   $ 2,172 $ 1,997 $ 1,914    
Common stock under employee stock purchase plan, par value   $ 10 $ 10   $ 0.10  
Shares of common stock purchased through the plan   49,668 47,229 35,950    
Employee Stock Purchase Plan            
Employee Stock Ownership Plan E S O P Disclosures [Line Items]            
Number of common stock shares under employee stock purchase plan 1,000,000          
Common stock under employee stock purchase plan, par value $ 0.10          
Employee stock purchase plan offering period   January 1 and July 1 of each year        
Employee stock purchase plan expiration date   Dec. 31, 2028        
Commons stock plan available for sale under plan           995,000
Available common stock under plan   593,962 643,630 690,859