Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	$ 201,646	$ 131,499
Unrealized Gains	237	168
Unrealized (Losses)	0	(3)
Fair Value	201,883	131,664
Less amounts classified as cash equivalents, Amortized Cost Basis	(64,370)	(4,960)	$ (11,954)
Marketable Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	137,753	128,348
Unrealized Gains	237	168
Unrealized (Losses)	0	(3)
Fair Value	137,990	128,513
Cash Equivalents
Cash And Cash Equivalents [Line Items]
Less amounts classified as cash equivalents, Amortized Cost Basis	(63,893)	(3,151)
Less amounts classified as cash equivalents, Fair Value	(63,893)	(3,151)
Money Market Funds
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	63,893	3,151
Unrealized Gains	0	0
Unrealized (Losses)	0	0
Fair Value	63,893	3,151
Commercial Paper
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	40,182	4,952
Unrealized Gains	0	0
Unrealized (Losses)	0	0
Fair Value	40,182	4,952
Corporate Debt Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	42,399	69,423
Unrealized Gains	81	79
Unrealized (Losses)	0	(3)
Fair Value	42,480	69,499
Asset-backed Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	8,573	27,005
Unrealized Gains	74	50
Unrealized (Losses)	0	0
Fair Value	8,647	27,055
U.S. Government Agencies
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	46,599	26,968
Unrealized Gains	82	39
Unrealized (Losses)	0	0
Fair Value	$ 46,681	$ 27,007