Net Loss Per Share - Anti-Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	12,499	12,059	12,478	12,059
Shares excluded as performance conditions not yet satisfied	16,400		16,400
Unvested Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive stock options not considered in computing diluted earnings per common share	417		396
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	12,082	12,059