Cash Equivalents and Short-term and Long-term Investments - Summary of Cash, Cash Equivalents and Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Cash and cash equivalents due in 90 days or less
Amortized Cost	$ 277,485	$ 237,677
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Estimated Fair Value	277,486	237,677	$ 214,490
Available-for-sale securities:
Amortized Cost	138,050	215,872
Gross Unrealized Gains	208	325
Gross Unrealized Losses	(181)	(28)
Estimated Fair Value	138,077	216,169
Total cash, cash equivalents and available-for-sale securities
Amortized Cost	415,535	453,549
Gross Unrealized Gains	209	325
Gross Unrealized Losses	(181)	(28)
Estimated Fair Value	415,563	453,846
Corporate obligations
Available-for-sale securities:
Amortized Cost	97,260	124,676
Gross Unrealized Gains	56	219
Gross Unrealized Losses	(181)	(15)
Estimated Fair Value	97,135	124,880
U.S. Treasury securities
Available-for-sale securities:
Amortized Cost	32,545	78,230
Gross Unrealized Gains	147	98
Gross Unrealized Losses	0	(1)
Estimated Fair Value	32,692	78,327
Certificates of deposit
Available-for-sale securities:
Amortized Cost	245	490
Gross Unrealized Gains	3	3
Gross Unrealized Losses	0	0
Estimated Fair Value	248	493
Mortgage and other asset backed securities
Available-for-sale securities:
Amortized Cost	8,000	12,476
Gross Unrealized Gains	2	5
Gross Unrealized Losses	0	(12)
Estimated Fair Value	$ 8,002	$ 12,469