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, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 3,505	$ 1,649	$ 3,472
Cash received from stock option exercises	7,697	3,281	3,325
Excess tax benefit from the exercise of stock options	576	259	877
Number of Shares
Beginning balance (in shares)	3,008
Granted (in shares)	666
Exercised (in shares)	(878)
Forfeited/expired (in shares)	(5)
Outstanding at December 31 (in shares)	2,791	3,008
Exercisable (in shares)	1,475
Ending vested and expected to vest (in shares)	2,710
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 12.60	$ 12.14
Granted (in dollars per share)	$ 12.59
Exercised (in shares)	$ 11.03
Forfeited/expired (in shares)	$ 13.52
Outstanding at December 31 (in dollars per share)	$ 12.60	$ 12.14
Exercisable (in dollars per share)	$ 12.44
Ending vested and expected to vest (in dollars per share)	$ 12.60
Outstanding, Remaining Contractual Term	3 years 7 months 25 days
Outstanding, Intrinsic Value	13,210
Exercisable, Remaining Contractual Term	3 years 6 months 31 days
Exercisable, Intrinsic Value	7,209
Ending vested and expected to vest, Remaining Contractual Term	1 year 11 months 5 days
Ending vested and expected to vest, Intrinsic Value	$ 12,833
Weighted average grant-date fair value of options granted	$ 4.27	$ 5.31	$ 5.28