Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								9 Months Ended		12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 6,744	$ 6,268	$ 6,268	$ 6,268	$ 6,282	$ 6,268	$ 6,288	$ 6,268			$ 25,548	$ 25,106	$ 21,837
Loss from operations	(12,242)	(11,069)	(8,526)	(7,046)	(6,498)	(5,110)	(6,123)	(5,264)			(38,883)	(22,995)	(16,631)
Net loss	(12,382)	(11,177)	(8,620)	(7,228)	(5,313)	(4,645)	(5,513)	(4,631)			(39,407)	(20,102)	(23,706)
Net loss applicable to common stockholders	$ (12,382)	$ (11,744)	$ (10,418)	$ (9,025)	$ (7,109)	$ (6,443)	$ (7,311)	$ (6,429)			$ (43,569)	$ (27,292)	$ (26,806)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.40)	$ (0.52)	$ (2.80)	$ (2.47)	$ (2.09)	$ (1.87)	$ (2.18)	$ (1.98)	$ (3.08)	$ (6.03)	$ (2.83)	$ (8.02)	$ (8.90)