Net Loss Per Common Share (Basic and Diluted Net Loss per Common Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net loss	$ (5,343)	$ (13,717)
Accretion of dividends on redeemable convertible preferred stock	0	2,605
Net loss attributable to common stockholders	$ (5,343)	$ (16,322)
Weighted-average common shares outstanding, basic and diluted	69,249,462	4,707,867
Net loss per common share, basic and diluted	$ (0.08)	$ (3.47)