Balance Sheet Components - Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash Equivalents and Marketable Securities
Total cash equivalents and marketable securities, Amortized Cost	$ 131,699	$ 127,540
Total cash equivalents and marketable securities, Gross Unrealized Gains	27
Total cash equivalents and marketable securities, Gross Unrealized Losses	(8)	(37)
Total cash equivalents and marketable securities, Fair Value	131,718	127,503
Corporate debt securities
Cash Equivalents and Marketable Securities
Total cash equivalents and marketable securities, Amortized Cost	33,653	8,997
Total cash equivalents and marketable securities, Gross Unrealized Gains	11
Total cash equivalents and marketable securities, Gross Unrealized Losses	(2)	(8)
Total cash equivalents and marketable securities, Fair Value	33,662	8,989
U.S. Treasury and agency securities
Cash Equivalents and Marketable Securities
Total cash equivalents and marketable securities, Amortized Cost	40,798	33,423
Total cash equivalents and marketable securities, Gross Unrealized Gains	14
Total cash equivalents and marketable securities, Gross Unrealized Losses	(2)	(29)
Total cash equivalents and marketable securities, Fair Value	40,810	33,394
Money Market Funds
Cash Equivalents and Marketable Securities
Total cash equivalents and marketable securities, Amortized Cost	12,964	25,390
Total cash equivalents and marketable securities, Fair Value	12,964	25,390
Commercial Paper
Cash Equivalents and Marketable Securities
Total cash equivalents and marketable securities, Amortized Cost	44,284	59,730
Total cash equivalents and marketable securities, Gross Unrealized Gains	2
Total cash equivalents and marketable securities, Gross Unrealized Losses	(4)
Total cash equivalents and marketable securities, Fair Value	$ 44,282	$ 59,730