Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013 Convertible notes payable [Member]	Sep. 30, 2013 Level 3 [Member] Common stock warrant liability [Member]	Sep. 30, 2013 Level 3 [Member] Preferred stock warrant liability [Member]	Sep. 30, 2013 Level 3 [Member] Convertible notes payable [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		$ 301,000	$ 1,884,000	$ 41,860,000
Warrants issued\ Convertible notes issued		900,000		9,069,000
Convertible notes cancelled				(1,360,000)
Accrued interest				1,299,000
Change in fair value recorded in change in fair value of financial instruments		377,000	(823,000)	(2,634,000)
Transfers out of Level 3	(48,234,000)	(434,000)	(140,000)	(48,234,000)
Reclassified to stockholders' equity (deficit)		(1,144,000)	(921,000)
Ending balance