Summary of Significant Accounting Policies - Reconciliation of Liabilities Measured at Fair Value Using Significant Observable Inputs (Level 3) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Warrants and Rights Outstanding [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 9,493	$ 345
Issuance		20,959
Exercises	(79)
Changes in fair value	21,927	(11,811)
Ending Balance	31,341	9,493
Embedded Derivative Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	992	845
Issuance		0
Exercises	0
Changes in fair value	(759)	147
Ending Balance	$ 233	$ 992