Debt Narratives (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Document Period End Date					Sep. 30, 2019
Debt, Weighted Average Interest Rate	4.69%				4.69%		4.99%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	70.00%				70.00%		66.00%
Interest Paid, Including Capitalized Interest, Operating and Investing Activities					$ 113,000	$ 113,100
Bank Credit Facility	$ 0				0		$ 387,061
Letters of Credit Outstanding, Amount	35,500				$ 35,500
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage					0.20%
Line of Credit Facility, Remaining Borrowing Capacity	729,500				$ 729,500
Line of Credit Facility, Increase (Decrease), Net	235,000			$ 55,000
Repayments of Long-term Debt					16,906	25,601
Losses on early extinguishment of debt, net	(9,058)		$ 0		(16,637)	(10,131)
Repayments of Debt					1,200,000	285,200
Repayments of Long-term Capital Lease Obligations					32,258	29,771
Redemption Premium	11,400
Letters of Credit Limit		$ 100,000		100,000
December 2022
Debt Instrument [Line Items]
Bank Credit Facility	0				0
Letters of Credit Outstanding, Amount							395,000
Repayments of Debt					32,100
Redemption Premium						9,600
May 2024
Debt Instrument [Line Items]
Bank Credit Facility	235,000				235,000		0
Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net		17,200
Repayments of Debt		32,100			8,500
Redemption Premium						25,300
Proceeds from Issuance of Debt		49,300		49,300
Line of Credit Facility, Maximum Borrowing Capacity		700,000		700,000
October 2018
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net						395,000
Repayments of Long-term Debt						$ 250,000
Bank Credit Facility due March 2022 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity		1,000,000		1,000,000
Repayments of Debt					450,000
Other Debt [Member]
Debt Instrument [Line Items]
Repayments of Debt					300
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,700,000		$ 1,700,000
Term Member 2024 [Member]
Debt Instrument [Line Items]
Term Loan	641,875				641,875		0
Repayments of Debt					8,100
Unsecured Debt | May 2024
Debt Instrument [Line Items]
Senior Notes	850,000				850,000		850,000
Unsecured Debt | June 2029 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 750,000				$ 750,000		$ 0