Fair Value Measurements - Schedule of Fair Value and Amortized Cost of Investments in Marketable Securities by Major Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 188,206	$ 259,833
Unrealized Gain	67
Unrealized Loss	(3)	(108)
Fair Value	188,270	259,725
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	45,498	45,017
Fair Value	45,498	45,017
U.S. Government Agency Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	74,801	103,957
Unrealized Gain	12
Unrealized Loss	(1)	(17)
Fair Value	74,812	103,940
Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	67,907	110,859
Unrealized Gain	55
Unrealized Loss	(2)	(91)
Fair Value	$ 67,960	$ 110,768