Stock Warrants (Details) (USD $)	3 Months Ended	12 Months Ended			12 Months Ended
	Sep. 30, 2010 Common stock warrant	Dec. 31, 2012 Common stock warrant	Dec. 31, 2011 Common stock warrant	Dec. 31, 2009 Common stock warrant	Dec. 31, 2012 Convertible preferred stock warrants	Dec. 31, 2011 Convertible preferred stock warrants	Dec. 31, 2010 Convertible preferred stock warrants
Warrants for the purchase of stock
Balance at the beginning of the period (in shares)		2,640,000	2,937,000	2,937,000	302,000	306,000	317,000
Conversion (in shares)		302,000			302,000
Expired (in shares)			(1,000)
Exercised (in shares)		(100,000)	(296,000)			(4,000)	(11,000)
Balance at the end of the period (in shares)		2,842,000	2,640,000	2,937,000		302,000	306,000
Weighted average exercise price
Balance at the beginning of the period (in dollars per share)		$ 2.98	$ 2.93	$ 2.35	$ 3.50	$ 3.48	$ 3.42
Conversion (in dollars per share)		$ 3.50			$ 3.50
Expired (in dollars per share)			$ 2.47
Exercised (in dollars per share)		$ 2.63	$ 2.46			$ 1.89	$ 1.89
Balance at the end of the period (in dollars per share)		$ 3.05	$ 2.98	$ 2.35		$ 3.50	$ 3.48
Additional disclosure
Number of warrants cashless exercised (in shares)		100,000
Number of common stock issued as a result of cashless exercise of warrants (in shares)		71,000
Number of warrants held by related party in which expiration and exercise price was modified (in shares)	2,596,000
Extended period of extension	4 years
Exercise price before modification, one (in dollars per share)	$ 2.12
Exercise price before modification, two (in dollars per share)	$ 2.47
Exercise price of warrants held by related party (in dollars per share)	$ 3.00
Incremental value of warrants accounted within additional paid-in capital	$ 1,803,000