Cash, Cash Equivalents and Short -Term Investments - Schedule of Cash, Cash Equivalents and Short-term Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	$ 325,211	$ 130,876	$ 143,841	$ 207,232
Short-Term Investments	120,625	124,112
Available For Sale
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	325,211	130,876
Short-Term Investments	120,625	124,112
Total	445,836	254,988
Available For Sale | Cash
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	61,623	32,123
Total	61,623	32,123
Available For Sale | Level 1 | Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	248,459	45,588
Total	248,459	45,588
Available For Sale | Level 1 | Time Deposits
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents		35,000
Total		35,000
Available For Sale | Level 2 | Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	9,535	15,666
Short-Term Investments	29,021	24,975
Total	38,556	40,641
Available For Sale | Level 2 | Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Short-Term Investments	68,829	78,998
Total	68,829	78,998
Available For Sale | Level 2 | U.S. Government and Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	5,594	2,499
Short-Term Investments	22,775	20,139
Total	$ 28,369	$ 22,638