Notes Payable - Additional Information (Detail) (2012 Notes [Member], USD $)	0 Months Ended	3 Months Ended	9 Months Ended
	Dec. 07, 2012 Note	Sep. 30, 2013	Sep. 30, 2013	Aug. 09, 2013	May 23, 2013	Mar. 28, 2013	Dec. 31, 2012
2012 Notes [Member]
Short-term Debt [Line Items]
Aggregate convertible notes authorized	$ 15,000,000			$ 18,000,000
Convertible notes, interest rate	8.00%
Convertible notes, maturity date			Sep. 30, 2013
Convertible notes, equity amount			15,000,000
Cash and cash equivalent threshold for requesting a subsequent closing		1,500,000	1,500,000
Number of individual convertible notes	5
Convertible notes, aggregate principal balance	3,000,000	3,000,000	3,000,000	4,500,000	4,500,000	3,000,000
Convertible notes authorized and available for sale							12,000,000
Additional convertible notes authorized				3,000,000
Convertible notes, amendment maturity date			Dec. 31, 2013
Fair value of embedded derivative		96,000	96,000
Unamortized debt discounts		3,600,000	3,600,000				669,000
Amortization of debt discount and accrued interest expense		$ 1,500,000	$ 2,900,000