Summary of Significant Accounting Policies - Reconciliation of Numerators and Denominators used in Computing Basic and Diluted Net Income Per Share (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accounting Policies [Abstract]
Net income (loss)	$ (4,015,881)	$ (10,895,976)	$ (13,814,639)	$ (20,561,356)
Numerator, basic and diluted net income (loss) available to stockholders	$ (4,015,881)	$ (10,895,976)	$ (13,814,639)	$ (20,561,356)
Shares used in computation - basic:
Weighted average common shares outstanding	84,898,133	79,345,030	84,420,661	78,350,236
Common shares outstanding for basic	84,898,133	79,345,030	84,420,661	78,350,236
Shares used in computation - diluted:
Common shares outstanding for basic	84,898,133	79,345,030	84,420,661	78,350,236
Shares used in computing diluted net income per share	84,898,133	79,345,030	84,420,661	78,350,236
Net (loss) per share - basic	$ (0.05)	$ (0.14)	$ (0.16)	$ (0.26)
Net (loss) per share - diluted	$ (0.05)	$ (0.14)	$ (0.16)	$ (0.26)