Common Stock and Stockholders' Deficit - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Stockholders Deficit [Line Items]
Common stock issued in exchange for proceeds upon the exercise of employee stock options			2,100,402
Proceeds upon the exercise of stock options			$ 1,500,000
Net income (loss)	2,713,000	(882,000)	4,450,000	(6,030,000)
Accumulated deficit	(53,187,000)		(53,187,000)		(57,637,000)
Stockholders' deficit	$ (41,357,000)		$ (41,357,000)		$ (50,813,000)
Series A Convertible Preferred Stock
Stockholders Deficit [Line Items]
Warrants exercise price	1.065		1.065
Warrants exercisable expiration date	2018-01		2018-01
Common stock warrants
Stockholders Deficit [Line Items]
Warrants exercisable expiration date	2021-02		2021-02
Common stock warrants | Scenario 1
Stockholders Deficit [Line Items]
Warrants exercise price	0.01		0.01
Common stock warrants | Scenario 2
Stockholders Deficit [Line Items]
Warrants exercise price	1.5677		1.5677