Employee Stock Purchase Plan Stock Options and Warrants - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 7,548	$ 3,505	$ 1,649
Cash received from stock option exercises	6,227	7,697	3,281
Excess tax benefit from the exercise of stock options	$ 2,124	$ 576	$ 259
Number of Shares
Beginning balance (in shares)	2,791
Granted (in shares)	618
Exercised (in shares)	(858)
Forfeited/expired (in shares)	(143)
Outstanding at December 31 (in shares)	2,408	2,791
Exercisable (in shares)				2,329
Ending vested and expected to vest (in shares)				992
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 14.25	$ 12.59		$ 14.25
Granted (in dollars per share)	18.16
Exercised (in dollars per share)	11.63
Forfeited/expired (in dollars per share)	14.38
Outstanding at December 31 (in dollars per share)	$ 14.25	$ 12.59
Exercisable (in dollars per share)				14.23
Ending vested and expected to vest (in dollars per share)				$ 13.34
Outstanding, remaining contractual term	4 years 3 months 35 days
Exercisable, remaining contractual term	4 years 3 months 20 days
Ending vested and expected to vest, remaining contractual term	2 years 10 months 10 days
Outstanding, intrinsic value				$ 10,752
Exercisable, intrinsic value				10,461
Ending vested and expected to vest, intrinsic value				$ 5,206