Summary of Significant Accounting Policies - Outstanding Options, Warrants and Restricted Stock Units (Detail) - shares	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Class of Stock [Line Items]
Outstanding options, warrants and restricted stock units	66,006,116	17,720,536
Options [Member]
Class of Stock [Line Items]
Outstanding options, warrants and restricted stock units	2,765,229	375,670
Restricted stock units [Member]
Class of Stock [Line Items]
Outstanding options, warrants and restricted stock units	9,358,518	3,137,440
Outstanding Warrants [Member]
Class of Stock [Line Items]
Outstanding options, warrants and restricted stock units	53,882,369	14,207,426