Net Loss per Common Share (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Basic and diluted net loss per common share calculation:
Net loss and comprehensive loss	$ (14,493,000)	$ (11,307,000)	$ 23,109,000
Net loss attributable to common stockholders	(14,831,000)	(11,621,000)
Accretion of redeemable convertible preferred stock	$ (338,000)	$ (314,000)
Weighted average common shares outstanding	212,290,406	182,535,562
Net loss per share of common stock—basic and diluted	$ (0.07)	$ (0.06)