Summary of Significant Accounting Policies (Potential Common Stock Equivalents Excluded from Calculation of Diluted Net Loss per Share) (Detail) - shares	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the calculation of diluted net loss per share	110,589,946	43,258,925
Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the calculation of diluted net loss per share	22,288,867	5,989,800
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the calculation of diluted net loss per share	88,301,079	37,269,125