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Summary of Significant Accounting Policies - Additional Information (Detail)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2020
USD ($)
Jun. 30, 2019
USD ($)
Jun. 30, 2020
USD ($)
segment
Jun. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
Jan. 01, 2020
USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Number of operating segments | segment     1      
Impairment of long lived assets $ 0 $ 0 $ 0 $ 0    
Operating lease right-of-use assets 43,137,000   43,137,000     $ 38,005,000
Operating lease liabilities 59,166,000   59,166,000     $ 53,800,000
Accounting Standards Update 2018-15            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Capitalized costs due to adoption of standard 1,300,000   2,700,000      
Fair Value, Inputs, Level 1 | Money market funds            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Fair value of money market instruments $ 324,700,000   324,700,000   $ 398,500,000  
Unrealized gains (losses) on money market instruments     $ 0   $ 0