Summary of Significant Accounting Policies - Summary of Impact of Restatement on Condensed Statement of Comprehensive Loss and Condensed Balance Sheets (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Net loss attributable to common stock	$ (4,135)	$ (2,266)	$ (6,015)	$ (4,157)
Basic and diluted net loss per share attributable to common stock	$ (1.86)	$ (1.65)	$ (2.89)	$ (3.10)
Weighted-average number of common shares outstanding	2,227	1,374	2,082	1,342
Additional paid-in capital	238,838		238,838		229,961
Accumulated deficit	(231,447)		(231,447)		(225,432)
Scenario, Previously Reported [Member]
Net loss attributable to common stock	(1,654)	(2,266)	(3,534)	(4,157)
Basic and diluted net loss per share attributable to common stock	$ (0.74)	$ (1.65)	$ (1.70)	$ (3.10)
Additional paid-in capital	236,357		236,357
Accumulated deficit	(228,966)		(228,966)
Restatement Adjustment [Member]
Net loss attributable to common stock	(2,481)		(2,481)
Basic and diluted net loss per share attributable to common stock	$ (1.12)	$ 0.00	$ (1.19)	$ 0.00
Additional paid-in capital	2,481		2,481
Accumulated deficit	$ (2,481)		$ (2,481)