Cash, Cash Equivalents and Short-Term Investments - Schedule of Securities Classified as Cash, Cash Equivalents and Short-Term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	$ 100,494	$ 181,133	$ 89,626	$ 78,768
Cash and cash equivalents, Amortized Cost		181,130
Cash and cash equivalents, Gross Unrealized Gains		3
Cash and cash equivalents, Fair Value	100,494	181,133
Short-term investments, Amortized Cost	104,030	66,362
Short-term investments, Gross Unrealized Gains	319	20
Short-term investments, Gross Unrealized Losses	(2)	(3)
Short-term investments, Fair Value	104,347	66,379
Cash equivalents and short-term investments, Amortized Cost	204,524	247,492
Cash equivalents and short-term investments, Gross Unrealized Gains	319	23
Cash equivalents and short-term investments, Gross Unrealized Losses	(2)	(3)
Cash equivalents and short-term investments, Fair Value	204,841	247,512
Money Market Funds [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	99,410	147,208
Cash and cash equivalents, Fair Value	99,410	147,208
Commercial Paper (Cash Equivalents) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost		19,357
Cash and cash equivalents, Gross Unrealized Gains		3
Cash and cash equivalents, Fair Value		19,360
US Government Agencies Short-term Debt Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	8,077
Short-term investments, Gross Unrealized Losses	(2)
Short-term investments, Fair Value	8,075
Corporate Bonds (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost		11,441
Cash and cash equivalents, Fair Value		11,441
Cash [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	1,084	3,124
Cash and cash equivalents, Fair Value	1,084	3,124
Commercial Paper (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	46,328	36,667
Short-term investments, Gross Unrealized Gains	115	14
Short-term investments, Fair Value	46,443	36,681
Corporate Bonds (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	35,119	21,690
Short-term investments, Gross Unrealized Gains	170	6
Short-term investments, Gross Unrealized Losses		(3)
Short-term investments, Fair Value	35,289	21,693
Asset-Backed Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	10,507	8,005
Short-term investments, Gross Unrealized Gains	25
Short-term investments, Fair Value	10,532	$ 8,005
U.S. Treasury Notes [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	3,999
Short-term investments, Gross Unrealized Gains	9
Short-term investments, Fair Value	$ 4,008