Financing Arrangements and Long-Term Debt (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2017
Line of Credit Facility [Line Items]
Amount outstanding		$ 325,000
Repayments of debt			$ 550,000	$ 600,000
Capital lease duration		25 years
Capital lease payment duration		15 years
Capital lease expiration date		Mar. 01, 2029
Capital lease obligations, current		$ 10,600
Capital lease obligations, noncurrent		125,800
Future maturities of long term debt in 2019		10,600
Future maturities of long term debt in 2020		11,200
Future maturities of long term debt in 2021		11,700
Future maturities of long term debt in 2022		1,100,000
Future maturities of long term debt in 2023		337,900
Thereafter		$ 1,760,000
5.75% Notes, Due August 15, 2025 [Member]
Line of Credit Facility [Line Items]
Interest rate					5.75%
Face amount of notes					$ 550,000
Maturity date		Aug. 15, 2025
Transaction costs					$ 8,400
3.50% notes, due December 2017 [Member]
Line of Credit Facility [Line Items]
Interest rate	3.50%
Repayments of debt	$ 550,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Amount outstanding		$ 24,700
2018 Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity		$ 1,600,000
Credit facility, expiration date		Nov. 01, 2023
Amount outstanding		$ 325,000
2018 Revolving Credit Facility [Member] | New York Federal Reserve Bank Rate [Member]
Line of Credit Facility [Line Items]
Spread above variable interest rate		0.50%
2018 Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Spread above variable interest rate		1.00%
2018 Revolving Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Facility fee arrears accrual rate		0.175%
2018 Revolving Credit Facility [Member] | Minimum [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Spread above variable interest rate		1.075%
2018 Revolving Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Facility fee arrears accrual rate		0.40%
2018 Revolving Credit Facility [Member] | Maximum [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Spread above variable interest rate		2.10%
Previous 2016 Senior Unsecured Credity Facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity			$ 1,100,000
Interest rate		3.831%