Cash Equivalents and Short-term and Long-term Investments - Summary of Cash, Cash Equivalents and Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Cash and cash equivalents due in 90 days or less
Amortized Cost	$ 283,522	$ 237,677
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Estimated Fair Value	283,521	237,677	$ 163,609
Available-for-sale securities:
Amortized Cost	106,099	215,872
Gross Unrealized Gains	199	325
Gross Unrealized Losses	(9)	(28)
Estimated Fair Value	106,289	216,169
Total cash, cash equivalents and available-for-sale securities
Amortized Cost	389,621	453,549
Gross Unrealized Gains	199	325
Gross Unrealized Losses	(10)	(28)
Estimated Fair Value	389,810	453,846
Corporate obligations
Available-for-sale securities:
Amortized Cost	56,828	124,676
Gross Unrealized Gains	162	219
Gross Unrealized Losses	(6)	(15)
Estimated Fair Value	56,984	124,880
U.S. Treasury securities
Available-for-sale securities:
Amortized Cost	49,026	78,230
Gross Unrealized Gains	33	98
Gross Unrealized Losses	(3)	(1)
Estimated Fair Value	49,056	78,327
Certificates of deposit
Available-for-sale securities:
Amortized Cost	245	490
Gross Unrealized Gains	4	3
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 249	493
Mortgage and other asset backed securities
Available-for-sale securities:
Amortized Cost		12,476
Gross Unrealized Gains		5
Gross Unrealized Losses		(12)
Estimated Fair Value		$ 12,469