Warrants (Detail) - Reconciliation of the warrant liability measured at fair value using Level 3 inputs (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Balance at beginning of period	$ 100	$ 1,238
Exercise of common stock warrants		(39)
Remeasurement of common stock warrants	6	(1,091)
Balance at end of period	$ 106	$ 108