Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basic and diluted net loss per common share calculation:
Net loss	$ (20,714)	$ (17,779)
Net loss attributable to common stockholders	$ (20,714)	$ (17,779)
Weighted average common shares outstanding (in shares)	56,894,672	51,350,365
Net loss per share of common stock—basic and diluted (in dollars per share)	$ (0.36)	$ (0.35)
Outstanding securities excluded from computation of diluted weighted shares outstanding as they would have been anti dilutive:
Outstanding securities excluded from computation of diluted weighted shares outstanding (in shares)	8,584,526	6,357,398
Options outstanding
Outstanding securities excluded from computation of diluted weighted shares outstanding as they would have been anti dilutive:
Outstanding securities excluded from computation of diluted weighted shares outstanding (in shares)	8,461,435	6,294,598
Warrants
Outstanding securities excluded from computation of diluted weighted shares outstanding as they would have been anti dilutive:
Outstanding securities excluded from computation of diluted weighted shares outstanding (in shares)	123,091	62,800