Stock-Based Compensation (Details) (Stock options, USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Stock options
Shares
Options Outstanding at beginning of the period (in shares)	5,349,810
Granted (in shares)	16,500
Exercised (in shares)	(275,251)
Canceled (in shares)	(5,750)
Options Outstanding at the end of the period (in shares)	5,085,309	5,349,810
Options Vested and Expected to Vest at the end of the period (in shares)	5,039,443
Options Exercisable at the end of the period (in shares)	3,158,304
Shares Available for Grant under the 2008 Plan (in shares)	3,341,331
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 5.98
Granted (in dollars per share)	$ 11.96
Exercised (in dollars per share)	$ 6.00
Canceled (in dollars per share)	$ 4.34
Options Outstanding at the end of the period (in dollars per share)	$ 6.00	$ 5.98
Options Vested and Expected to Vest at the end of the period (in dollars per share)	$ 6.01
Options Exercisable at the end of the period (in dollars per share)	$ 6.68
Weighted Average Remaining Contractual Term
Options Outstanding at beginning of the period	6 years 9 months 18 days	7 years
Options Outstanding at the end of the period	6 years 9 months 18 days	7 years
Options Vested and Expected to Vest at the end of the period	6 years 8 months 12 days
Options Exercisable at the end of the period	5 years 6 months
Additional information
Weighted average grant-date fair value (in dollars per share)	$ 7.64