Warrants (Detail) - Reconciliation of the warrant liability measured at fair value using Level 3 inputs (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Balance at beginning of period	$ 10	$ 100
Remeasurement of common stock warrants	(3)	141
Balance at end of period	$ 7	$ 241