Outstanding Options, Vested Options and Options Vested and Expected to Vest (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Issued and Outstanding, Options Outstanding	10,828,682	10,255,222
Stock Options Issued and Outstanding, Vested Options	3,875,734
Stock Options Issued and Outstanding, Options Vested and Expected to Vest	10,362,887
Weighted Average Remaining Contractual Life, Options Outstanding	8 years 26 days
Weighted Average Remaining Contractual Life, Vested Options	6 years 11 months 5 days
Weighted Average Remaining Contractual Life, Options Vested and Expected to Vest	8 years 11 days
Weighted Average Exercise Price, Options Outstanding	$ 3.76	$ 1.19
Weighted Average Exercise Price, Vested Options	$ 0.96
Weighted Average Exercise Price, Options Vested and Expected to Vest	$ 3.63