Employee Stock Purchase Plan Stock Options and Warrants - Stock Option Activity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 3,472	$ 9,433	$ 1,928
Cash received from stock option exercises	3,325	7,197	1,330
Net income tax benefit from the exercises of stock options	877	3,122	399
Number of Shares
Beginning balance (in shares)	4,077
Granted (in shares)	128	844	125
Exercised (in shares)	(610)
Forfeited/expired (in shares)	(60)
Outstanding at December 31 (in shares)	3,535	4,077
Exercisable (in shares)	2,521
Ending vested and expected to vest (in shares)	3,521
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 12.55	$ 11.96
Granted (in dollars per share)	$ 13.04
Exercised (in shares)	$ 8.51
Forfeited/expired (in shares)	$ 14.82
Outstanding at December 31 (in dollars per share)	$ 12.55	$ 11.96
Exercisable (in dollars per share)	$ 12.55
Ending vested and expected to vest (in dollars per share)	$ 12.21
Outstanding, Remaining Contractual Term	3 years 0 months 11 days
Outstanding, Intrinsic Value	6,161
Exercisable, Remaining Contractual Term	3 years 0 months 7 days
Exercisable, Intrinsic Value	6,156
Ending vested and expected to vest, Remaining Contractual Term	2 years 2 months 1 day
Ending vested and expected to vest, Intrinsic Value	$ 5,635
Weighted average grant-date fair value of options granted	$ 5.31	$ 5.28	$ 5.64