Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data	Total	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance, Value at Dec. 31, 2010	$ (29,591)	$ 32,940	$ 5,681		$ 3	$ 643	$ (8)	$ (30,229)
Beginning balance, Shares at Dec. 31, 2010		33,188,889	5,190,551		2,837,967
Unrealized gain/loss on marketable securities	31						31
Net loss	(23,706)							(23,706)
Issuance of stock, Value				77,301
Issuance of stock, Shares				15,882,389
Stock-based compensation expense	371					371
Vesting of restricted stock, Value	56					56
Vesting of restricted stock, Shares					181,818
Issuance of common stock upon exercise of stock options, Value	57					57
Issuance of common stock upon exercise of stock options, Shares					177,635
Ending balance, Value at Dec. 31, 2011	(52,782)	32,940	5,681	77,301	3	1,127	23	(53,935)
Ending balance, Shares at Dec. 31, 2011		33,188,889	5,190,551	15,882,389	3,197,420
Unrealized gain/loss on marketable securities	(25)						(25)
Net loss	(20,102)							(20,102)
Stock-based compensation expense	742					742
Vesting of restricted stock, Value	56					56
Vesting of restricted stock, Shares					183,713
Issuance of common stock upon exercise of stock options, Value	87					87
Issuance of common stock upon exercise of stock options, Shares					234,968
Ending balance, Value at Dec. 31, 2012	(72,024)	32,940	5,681	77,301	3	2,012	(2)	(74,037)
Ending balance, Shares at Dec. 31, 2012		33,188,889	5,190,551	15,882,389	3,616,101
Unrealized gain/loss on marketable securities	16						16
Net loss	(39,407)							(39,407)
Issuance of stock, Value	110,980				7	110,973
Issuance of stock, Shares					6,772,221
Stock-based compensation expense	3,030					3,030
Vesting of restricted stock, Value	64					64
Vesting of restricted stock, Shares					136,758
Issuance of common stock upon exercise of stock options, Value	150					150
Issuance of common stock upon exercise of stock options, Shares	237,565				237,565
Conversion of convertible preferred stock upon initial public offering, Value	115,923	(32,940)	(5,681)	(77,301)	20	115,903
Conversion of convertible preferred stock upon initial public offering, Shares		(33,188,889)	(5,190,551)	(15,882,389)	19,731,564
Issuance of Common Stock for private placement, Value	12,750				1	12,749
Issuance of Common Stock for private placement, Shares					708,333
Ending balance, Value at Dec. 31, 2013	$ 131,482				$ 31	$ 244,881	$ 14	$ (113,444)
Ending balance, Shares at Dec. 31, 2013					31,202,542