Stock-Based Compensation Plans ESPP (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	1,492,088
Employee Stock Purchase Plan (ESPP), Compensation Expense	$ 17,477	$ 17,888	$ 14,301
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	1,265,625
ESPP, Purchase Price of Common Stock, Percent	90.00%
Total stock issued under ESPP since inception	278,230
ESPP, Description	10% purchase discount
Employee Stock Purchase Plan (ESPP), Compensation Expense	$ 200	$ 200	$ 200