Stock Options, Restricted Stock and Employee Stock Purchase Plan - Stock Option Activity (Details) - Stock Option Plan 2014 And 2003 - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Beginning balance, outstanding (in Shares)	4,766	4,762	6,386
Granted (in Shares)	66	2,089	1,016
Exercised (in Shares)	(623)	(1,794)	(2,519)
Forfeited or expired (in Shares)	(156)	(291)	(121)
Ending balance, outstanding (in Shares)	4,053	4,766	4,762
Number of Shares, Exercisable (in Shares)	1,845
Weighted Average Exercise Price
Beginning balance, outstanding (in Dollars per share)	$ 27.27	$ 20.33	$ 11.44
Granted (in Dollars per share)	21.28	26.61	37.60
Exercised (in Dollars per share)	15.53	7.78	4.09
Forfeited or expired (in Dollars per share)	28.20	28.96	34.78
Ending balance, outstanding (in Dollars per share)	28.95	$ 27.27	$ 20.33
Weighted Average Exercise Price, Exercisable (in Dollars per share)	$ 29.15
Weighted Average Remaining Contractual Term (Years)	4 years 6 months 23 days
Weighted Average Remaining Contractual Term, Exercisable (Years)	3 years 11 months 10 days
Aggregate Intrinsic Value	$ 21,459
Aggregate Intrinsic Value, Exercisable	$ 10,103