Cash Equivalents and Marketable Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 402,121	$ 381,742
Debt Securities, Available-for-sale [Line Items]
Unrealized Gains	789	172
Unrealized Losses	(1)	(6)
Cash and cash equivalents and available-for-sale securities, amortized cost	484,164	466,519
Cash, cash equivalents, and available-for-sale securities	484,952	466,685
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,959
Unrealized Gains	0
Unrealized Losses	0
Aggregate Fair Value	8,959
U.S. treasury debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	20,860	10,342
Unrealized Gains	190	8
Unrealized Losses	0	(1)
Aggregate Fair Value	21,050	10,349
U.S. corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	75,844	95,706
Unrealized Gains	599	164
Unrealized Losses	(1)	(5)
Aggregate Fair Value	76,442	95,865
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	378,501	360,471
Cash and cash equivalents, aggregate fair value	378,501	360,471
Cash and cash equivalents
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	378,501	360,471
Cash and cash equivalents, aggregate fair value	378,501	360,471
Marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	105,663	106,048
Unrealized Gains	789	172
Unrealized Losses	(1)	(6)
Aggregate Fair Value	$ 106,451	$ 106,214