Financings - Follow-on Underwritten Public Offering (Detail) (USD $)	1 Months Ended
	May 07, 2013	Sep. 30, 2013
Equity [Line Items]
Combined price per share		$ 1.55
Common Stock [Member]
Equity [Line Items]
Number of shares of common stock sold in financing	17,500,000
Common Stock and Matching Warrants Sold [Member]
Equity [Line Items]
Combined price per share	$ 0.50
Common Stock and Matching Warrants Sold [Member] | Common Stock [Member]
Equity [Line Items]
Number of shares of common stock sold in financing	17,500,000
Pre-funded Warrants and Matching Warrants Sold [Member]
Equity [Line Items]
Combined price per share	$ 0.49
Matching Warrants [Member]
Equity [Line Items]
Total (shares)	33,316,327
Warrant exercise price (per share)	0.47
Term of warrant (years)	5 years
Matching Warrants [Member] | Common Stock and Matching Warrants Sold [Member]
Equity [Line Items]
Total (shares)	17,500,000
Matching Warrants [Member] | Pre-funded Warrants and Matching Warrants Sold [Member]
Equity [Line Items]
Total (shares)	15,816,327
Pre-funded Warrants [Member]
Equity [Line Items]
Total (shares)	15,816,327	4,175,975
Warrant exercise price (per share)	0.01	0.01
Term of warrant (years)	7 years
Pre-funded Warrants [Member] | Pre-funded Warrants and Matching Warrants Sold [Member]
Equity [Line Items]
Total (shares)	15,816,327