Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments [Member]
Schedule of Financial Instruments [Line Items]
Due within one year	$ 185,550	$ 153,802
Amortized Cost	185,439	153,648
Unrealized Gains, net	111	154
Fair Value	185,550	153,802
Money Market Funds [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	151,266	109,265
Fair Value	151,266	109,265
Certificate of Deposit [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	7,030	7,000
Fair Value	7,030	7,000
Corporate Bonds [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	9,785	15,194
Unrealized Gains, net	20	40
Fair Value	9,805	15,234
Commercial Paper [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	7,503	9,889
Unrealized Gains, net		76
Fair Value	7,503	9,965
U.S. Treasury Securities [Member]
Schedule of Financial Instruments [Line Items]
Amortized Cost	9,855	12,300
Unrealized Gains, net	91	38
Fair Value	$ 9,946	$ 12,338