Description of the Business and Liquidity (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Mar. 31, 2019
Liquidity
Accumulated deficit	$ (181,453)	$ (193,936)
Secondary public offering
Liquidity
Issuance of common stock in connection with secondary public offering (in shares)	12,000,000
Proceeds from issuance of common stock, net of issuance costs	$ 42,100