Stockholders' Equity - At The Market Issuances (Details) - At-The-Market Issuance Sales Agreement - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended	42 Months Ended
	Oct. 31, 2015	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Stockholders' Equity (Deficit)
Number of shares sold by the entity		0	0	597,256
Value of shares sold by the entity				$ 9.6
Net proceeds after deducting commissions and other transactions costs				9.4
Remaining reserved amount under shelf registration		$ 90.4		$ 90.4
Cowen & Co. LLC | Maximum
Stockholders' Equity (Deficit)
Maximum aggregate offering price	$ 100.0
Percentage of gross proceeds payable as commission	3.00%
Notice period of termination of sales agreement	10 days