Stock Based Compensation - Summary of Stock Option Transactions under Company's Stock Incentive Plans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Outstanding, Beginning Balance	7,996,569	6,955,100	5,186,105
Shares, Granted	2,876,382	1,687,257	2,052,000
Shares, Exercised	(347,450)	(96,345)	(74,386)
Shares, Forfeited	(2,121,313)	(549,443)	(208,619)
Shares Outstanding, Ending Balance	8,404,188	7,996,569	6,955,100
Shares Vested and unvested options expected to vest as of December 31, 2013	8,091,725
Weighted Average Exercise Price, Beginning Balance	$ 3.36	$ 3.51	$ 4.06
Weighted Average Exercise Price, Granted	$ 2.56	$ 3.50	$ 2.34
Weighted Average Exercise Price, Exercised	$ 2.34	$ 2.29	$ 2.85
Weighted Average Exercise Price, Forfeited	$ 3.27	$ 5.94	$ 5.77
Weighted Average Exercise Price, Ending Balance	$ 3.15	$ 3.36	$ 3.51
Weighted Average Exercise Price, Vested and unvested options expected to vest as of December 31, 2013	$ 3.16