Annual report pursuant to Section 13 and 15(d)

Leases - Additional Information (Detail)

v3.20.4
Leases - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Jan. 01, 2019
Lessee, Lease, Description [Line Items]        
Right-of-use assets $ 52,200,000 $ 36,500,000    
Total lease liabilities - Operating leases $ 53,963,000 $ 37,200,000    
Operating Lease, Liability, Statement of Financial Position [Extensible List] us-gaap:AccruedLiabilitiesAndOtherLiabilities us-gaap:AccruedLiabilitiesAndOtherLiabilities    
Net rental expenses $ 8,500,000 $ 7,900,000 $ 7,400,000  
Weighted average remaining lease term 8 years 9 months 8 years 6 months 25 days    
Weighted average discount rate (percent) 2.43% 3.24%    
Net lease expense $ 8,500,000 $ 7,900,000    
Operating lease costs 8,500,000 8,000,000.0    
Sublease income 132,000 132,000    
Cash paid for amounts included in the measurement of Company's operating lease liabilities $ 7,600,000 $ 7,200,000    
ASU 2016-02        
Lessee, Lease, Description [Line Items]        
Right-of-use assets       $ 40,900,000
Total lease liabilities - Operating leases       $ 40,900,000
Minimum        
Lessee, Lease, Description [Line Items]        
Operating lease remaining term 1 year      
Finance lease remaining term 1 year      
Maximum        
Lessee, Lease, Description [Line Items]        
Operating lease remaining term 13 years      
Finance lease remaining term 13 years      
Operating lease extension term 5 years      
Finance lease extension term 5 years