Net Loss Per Share - Anti-Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	16,342	12,059	13,827	12,059
Shares excluded as performance conditions not yet satisfied	16,300		16,300
Unvested Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	513		483
Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	3,322		1,119
Common Stock Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	12,507	12,059	12,225	12,059