Stock-Based Compensation Plans ESPP (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	1,911,447
Employee Stock Purchase Plan (ESPP), Compensation Expense	$ 17.9	$ 14.3	$ 12.7
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	257,611
ESPP, Description	10% purchase discount
Employee Stock Purchase Plan (ESPP), Compensation Expense	$ 0.2	$ 0.1	$ 0.1