Equity Incentive Plans (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Summary of the activity of stock option awards
Options outstanding, Beginning Balance, Shares	1,198
Options outstanding, Beginning Balance, Wtd. Avg. Exercise Price	$ 18.92
Options outstanding, Beginning Balance, Wtd. Avg., Remaining Contractual Term	6 years 11 months 12 days	6 years 10 months 6 days
Options outstanding, Beginning Balance, Aggregate Intrinsic Value	$ 11,090
Options granted, Shares	0
Options granted, Wtd. Avg. Exercise Price	$ 0.00
Options exercised, Shares	(181)
Options exercised, Wtd. Avg. Exercise Price	$ 16.81
Options forfeited/canceled/expired, Shares	3
Options forfeited/canceled/expired, Wtd. Avg. Exercise Price	$ 20.67
Options outstanding, Ending Balance, Shares	1,014	1,198
Options outstanding, Ending Balance, Wtd. Avg. Exercise Price	$ 19.30	$ 18.92
Options outstanding, Ending Balance, Wtd. Avg., Remaining Contractual Term	6 years 11 months 12 days	6 years 10 months 6 days
Options outstanding, Ending Balance, Aggregate Intrinsic Value	18,567	11,090
Options vested and expected to vest at March 31, 2013, Shares	977
Options vested and expected to vest at March 31, 2013, Wtd. Avg. Exercise Price	$ 19.22
Options vested and expected to vest at March 31, 2013, Wtd. Avg., Remaining Contractual Term	6 years 10 months 24 days
Options vested and expected to vest at March 31, 2013, Aggregate Intrinsic Value	17,975
Options exercisable at March 31, 2013 Shares	637
Options exercisable at March 31, 2013, Wtd. Avg. Exercise Price	$ 18.27
Options exercisable at March 31, 2013, Wtd. Avg. Remaining Contractual Term	6 years 3 months 26 days
Options exercisable at March 31, 2013, Aggregate Intrinsic Value	$ 12,322