Common Stock (Details) - USD ($) $ in Thousands			3 Months Ended		29 Months Ended
	Apr. 05, 2019	Nov. 30, 2016	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2019	Dec. 31, 2019	Feb. 25, 2019
Common Stock
Common stock, shares authorized			100,000,000			100,000,000
Net proceeds from issuance of common stock			$ 12,690	$ 4,954
2019 Sales Agreement
Common Stock
Number of shares issued			9,995,282
Net proceeds from issuance of common stock			$ 45,316
Common Stock
Common Stock
Number of shares issued			2,657,823	1,318,481
Common Stock | 2016 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering		$ 40,000
Number of shares issued				1,318,481	6,330,222
Net proceeds from issuance of common stock				$ 4,954	$ 38,381
Aggregate value available for issuance							$ 0
Common Stock | 2019 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering	$ 50,000
Number of shares issued			2,657,823
Net proceeds from issuance of common stock			$ 12,690