Net Loss Per Share - Anti-Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	12,546	12,059
Shares excluded as performance conditions not yet satisfied	26,400	0
Unvested Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	464
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	12,082	12,059