Summarized Quarterly Data (Unaudited) - Summary of Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended							6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Information Disclosure [Abstract]
Net revenues				$ 15,183	$ 18,713	$ 17,186	$ 14,769
Loss from operations	$ (17,721)	$ (22,225)	$ (23,988)	(9,887)	(6,844)	(6,830)	(6,356)	$ (46,213)	$ (63,934)	$ (89,064)	$ (29,917)	$ (23,683)
Net loss	$ (33,892)	$ (36,997)	$ (26,233)	$ (12,105)	$ (10,872)	$ (11,916)	$ (11,451)	$ (63,230)	$ (97,122)	$ (138,696)	$ (46,344)	$ (24,197)
Loss per common share, basic (usd per share)	$ (1.04)	$ (1.13)	$ (0.81)	$ (0.39)	$ (0.35)	$ (0.39)	$ (0.37)	$ (1.94)	$ (2.98)	$ (4.22)	$ (1.50)	$ (0.86)
Loss per common share, diluted (usd per share)	$ (1.04)	$ (1.13)	$ (0.81)	$ (0.39)	$ (0.35)	$ (0.39)	$ (0.37)	$ (1.94)	$ (2.98)	$ (4.22)	$ (1.50)	$ (0.86)