Stockholders' Equity - Additional Information (Detail) - USD ($)						12 Months Ended
	Dec. 06, 2013	Jan. 31, 2012	Nov. 30, 2011	Oct. 02, 2009	Dec. 27, 2007	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Mar. 30, 2014	Dec. 31, 2011	Dec. 31, 2009	Dec. 06, 2009	Dec. 31, 2008	Dec. 31, 2007	Jul. 12, 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in common stock, shares authorized		3,459,900	88,227,450	24,219,300	2,883,250
Common stock, shares authorized						750,000,000	750,000,000		130,322,900			126,863,000	38,635,550			14,416,250	11,533,000
Common stock, shares issued						100,180,872	63,182,806		5,391,095	48,855,255	244,276,923
Common stock, par or stated value per share	$ 0.001					$ 0.001	$ 0.001		$ 0.001	$ 0.001
Preferred stock, shares authorized	25,000,000				6,500,000				65,693,245			62,693,245	21,734,402
Increase in preferred stock, shares authorized		3,000,000	40,958,843	15,234,402
Preferred stock, par or stated value per share	$ 0.01
Dividends, preferred stock, total						$ 0	$ 0	$ 0
Preferred stock redemption percentage							25.00%
Preferred stock, accretion of redemption discount						$ 0	$ 0	40,000
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion of stock, amount issued	15,139,409
Series A Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock shares, issued									5,696,261			5,734,402			3,373,882	3,143,749
Preferred stock, par or stated value per share									$ 3.49			$ 3.49			$ 3.49	$ 3.49
Preferred stock shares, outstanding									5,696,261			5,734,402			3,373,882
Conversion of stock, shares converted									38,141
Stock conversion price							$ 3.49
Series B Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock shares, issued														11,504,298
Preferred stock, par or stated value per share														$ 3.49
Conversion of stock, shares converted									49,998
Stock conversion price							3.49
Preferred stock, accretion of redemption discount								(31,000)
Series B-1 Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock shares, issued									45,998,220			45,121,691
Preferred stock, par or stated value per share									$ 0.33			$ 0.33
Preferred stock shares, outstanding									45,998,220			45,121,691
Stock conversion price							$ 0.33
Preferred stock, accretion of redemption discount								$ (9,000)
Series B Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion of stock, amount issued								7,569,704.4
Series B Redeemable Convertible Preferred Stock [Member] | Private Placement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share price								$ 4.00