Cash Equivalents and Investments - Schedule of Fair Value of Securities, not Including Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 141,934	$ 73,427
Gross Unrealized Gains	83	3
Gross Unrealized Losses	(1)	(19)
Estimated Fair Value	142,016	73,411
Classified as:
Cash equivalents	13,897	15,091
Short-term investments	120,089	58,320
Long-term investments	8,030	0
Total cash equivalents and available-for-sale investments	142,016	73,411
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,329	9,976
Gross Unrealized Gains	72	0
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	77,400	9,975
Corporate notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	14,955	16,514
Gross Unrealized Gains	11	3
Gross Unrealized Losses	0	(18)
Estimated Fair Value	14,966	16,499
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35,753	36,331
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	35,753	36,331
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	13,897	10,606
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 13,897	$ 10,606