Cash, Cash Equivalents and Marketable Securities - Amortized Cost and Fair Value of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash	$ 23,887	$ 43,058
Total cash equivalents	143,029
Total cash and cash equivalents	166,916	62,070
Amortized Cost	338,004	188,706
Gross Unrealized Gains	190	381
Gross Unrealized Losses	(1)	(2)
Marketable securities	338,193	189,085
Total cash, cash equivalents and marketable securities	504,920	250,776
Total cash, cash equivalents and marketable securities at fair value	505,109	251,155
Money market funds
Cash and Cash Equivalents [Line Items]
Total cash equivalents	80,986	11,527
Commercial paper
Cash and Cash Equivalents [Line Items]
Total cash equivalents	61,043	7,485
Amortized Cost	210,986	73,366
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Marketable securities	210,986	73,366
Certificates of deposits
Cash and Cash Equivalents [Line Items]
Total cash equivalents	1,000
Amortized Cost	44,480	41,302
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Marketable securities	44,480	41,302
U.S Treasury securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	43,050
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)
Marketable securities	43,050
U.S. Government-sponsored enterprises debt securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	6,200
Gross Unrealized Gains	17
Gross Unrealized Losses	0
Marketable securities	6,217
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	33,288	74,038
Gross Unrealized Gains	172	381
Gross Unrealized Losses	0	(2)
Marketable securities	$ 33,460	$ 74,417