Fair Value Measurement - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 307,963	$ 322,455
Short-term investments	468	288
Deferred compensation plan investments	1,602	1,110
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	307,963	322,455
Short-term investments	0	0
Deferred compensation plan investments	1,602	1,110
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	468	288
Deferred compensation plan investments	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Deferred compensation plan investments	$ 0	$ 0