Fair Value of Financial Assets and Liabilities - By Type (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Marketable securities:
Amortized Cost	$ 24,949	$ 39,074
Gross Unrealized Gain	67	7
Gross Unrealized Loss	(3)	(3)
Fair Value	25,013	39,078
Corporate debt securities
Marketable securities:
Amortized Cost	3,835	7,815
Gross Unrealized Gain		2
Gross Unrealized Loss	(3)
Fair Value	3,832	7,817
Commercial paper
Marketable securities:
Amortized Cost	9,061	15,129
Fair Value	9,061	15,129
Asset-backed securities
Marketable securities:
Amortized Cost	2,002	8,004
Gross Unrealized Gain		4
Fair Value	2,002	8,008
U.S. government agency debt securities
Marketable securities:
Amortized Cost	10,051	8,126
Gross Unrealized Gain	67	1
Gross Unrealized Loss		(3)
Fair Value	$ 10,118	$ 8,124