Net Loss Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		81 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Basic and diluted net loss per common share calculation:
Net loss	$ (16,132)	$ (4,153)	$ (30,757)	$ (10,731)	$ (131,387)
Accretion of preferred stock dividends	(2,292)	(1,775)	(5,891)	(5,288)	(33,046)
Net loss attributable to common stockholders	$ (18,424)	$ (5,928)	$ (36,648)	$ (16,019)	$ (164,433)
Weighted average common shares outstanding	1,795	1,455	1,579	1,447
Net loss per share of common stock - basic and diluted (in dollars per share)	$ (10.26)	$ (4.07)	$ (23.21)	$ (11.07)
Anti-dilutive securities
Total (in shares)	2,721	17,892	2,721	17,892
Redeemable convertible preferred stock
Anti-dilutive securities
Total (in shares)		16,513		16,513
Stock options
Anti-dilutive securities
Total (in shares)	2,620	1,301	2,620	1,301
Warrants
Anti-dilutive securities
Total (in shares)	101	78	101	78