Net Loss Per Share - Anti-Dilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	12,340	12,059	12,059
Unvested Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	258
Shares excluded as performance conditions not yet satisfied	25,700
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	12,059