Stock Based Compensation - Summary of Stock Option Transactions under Company's Stock Incentive Plans (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Outstanding, Beginning Balance	8,594,432	8,404,188	7,996,569
Shares, Granted	2,356,750	1,889,614	2,876,382
Shares, Exercised	0	0	(347,450)
Shares, Forfeited	(1,495,344)	(1,699,370)	(2,121,313)
Shares Outstanding, Ending Balance	9,455,838	8,594,432	8,404,188
Shares Vested and unvested options expected to vest as of December 31, 2015	9,235,450
Weighted Average Exercise Price, Beginning Balance	$ 2.66	$ 3.15	$ 3.36
Weighted Average Exercise Price, Granted	1.01	1.40	2.56
Weighted Average Exercise Price, Exercised	0	0	2.34
Weighted Average Exercise Price, Forfeited	2.15	3.69	3.27
Weighted Average Exercise Price, Ending Balance	2.33	$ 2.66	$ 3.15
Weighted Average Exercise Price, Vested and unvested options expected to vest as of December 31, 2015	$ 2.35