Warrants (Detail) - Reconciliation of the warrant liability measured at fair value using Level 3 inputs (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Balance at beginning of year	$ 100	$ 1,238
Exercise of common stock warrants		(39)
Remeasurement of common stock warrants	(90)	(1,099)
Balance at end of year	$ 10	$ 100