Warrants (Detail) - Reconciliation of the warrant liability measured at fair value using Level 3 inputs (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Balance at beginning of period	$ 100	$ 1,238
Exercise of common stock warrants		(39)
Remeasurement of common stock warrants	59	(1,072)
Balance at end of period	$ 159	$ 127