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, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 3,648	$ 7,548	$ 3,505
Cash received from stock option exercises	4,577	6,227	7,697
Excess tax benefit from the exercise of stock options	$ 669	$ 2,124	$ 576
Number of Shares
Beginning balance (in shares)	2,408
Granted (in shares)	880
Exercised (in shares)	(362)
Forfeited/expired (in shares)	(109)
Outstanding at December 31 (in shares)	2,817	2,408
Exercisable (in shares)				1,033
Ending vested and expected to vest (in shares)				2,718
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 15.32	$ 14.26		$ 15.32
Granted (in dollars per share)	17.43
Exercised (in dollars per share)	13.61
Forfeited/expired (in dollars per share)	14.52
Outstanding at December 31 (in dollars per share)	$ 15.32	$ 14.26
Exercisable (in dollars per share)				13.64
Ending vested and expected to vest (in dollars per share)				$ 15.27
Outstanding, remaining contractual term	4 years 5 months 10 days
Exercisable, remaining contractual term	2 years 8 months 8 days
Ending vested and expected to vest, remaining contractual term	4 years 4 months 25 days
Outstanding, intrinsic value				$ 31,476
Exercisable, intrinsic value				13,274
Ending vested and expected to vest, intrinsic value				$ 30,512