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Recent Accounting Standards - Additional Information (Detail) - USD ($)
Jan. 01, 2019
Dec. 31, 2020
Dec. 31, 2019
Jan. 01, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Retained earnings   $ 575,965,000 $ 583,489,000  
Short-term investments   0 108,919,000  
Right-of-use assets   73,597,000 $ 85,538,000  
Operating lease liabilities, Total   $ 95,141,000    
Minimum | US Treasury Securities        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Available-for-sale securities maturity range   3 months    
Maximum | US Treasury Securities        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Available-for-sale securities maturity range   1 year    
ASU 2016-13 | Revision of Prior Period, Change in Accounting Principle, Adjustment        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Retained earnings   $ 0    
ASU 2018-15        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Material capitalized implementation costs   $ 0    
ASU 2016-02        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Retained earnings $ 0      
Right-of-use assets 88,800,000      
Operating lease liabilities, Total 116,900,000      
Reductions in deferred rent 28,500,000      
Reductions in prepaid expenses $ 400,000      
ASU 2016-16 | Revision of Prior Period, Change in Accounting Principle, Adjustment        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Retained earnings       $ 0