Financing Arrangements and Debt (Narrative) (Details)	6 Months Ended
	Jun. 30, 2018 USD ($)
Line of Credit Facility [Line Items]
Capital Lease Duration	25 years
Capital lease payment duration	15 years
Capital lease expiration date	Mar. 31, 2029
Capital lease obligations, current	$ 9,700,000
Capital lease obligations, noncurrent	122,900,000
2016 Senior Unsecured Guaranteed Credity Facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity	$ 1,100,000,000
Credit facility, expiration date	Aug. 01, 2021
Amount outstanding	$ 0
2016 Senior Unsecured Guaranteed Credity Facility [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Interest rate	5.5375%
2016 Senior Unsecured Guaranteed Credity Facility [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Amount outstanding	$ 27,900,000