Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Warrant [Member]	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of Common stock	3,322,500
Share price	$ 3.00
Gross proceeds	$ 10.0
Net proceeds from public offering	9.2
Underwriting fees and offering costs	$ 0.8
Stock option to purchase		5,614,342
Exercise prices per share					$ 0.25	$ 3.98
Warrants to purchase common stock, shares		48,962,275	45,280,280	1,358,333
Warrants, exercise price					$ 0.75	$ 1.50