Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator:
Net income	$ 3,664	$ 2,401	$ 12,158	$ 13,934
Non-cumulative dividends to holders of preferred stock		(1,498)	(2,248)	(4,495)
Undistributed earnings allocable to holders of preferred stock		(840)	(3,709)	(8,821)
Net income-basic	3,664	63	6,201	618
Adjustment for undistributed earnings reallocated to holders of common stock		145	521	1,221
Net income-diluted	$ 3,664	$ 208	$ 6,722	$ 1,839
Weighted average shares used in computing net income per share:
Basic	20,342	982	10,956	925
Weighted average effect of potentially dilutive securities:
Options to purchase common stock	2,699	2,820	2,789	2,271
Employee stock purchase plan	117		70
Common stock warrants	1		1
Convertible preferred stock warrants
Diluted	23,159	3,802	13,816	3,196
Net income per share:
Basic	$ 0.18	$ 0.06	$ 0.57	$ 0.67
Diluted	$ 0.16	$ 0.05	$ 0.49	$ 0.58