Debt Narratives (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Document Period End Date	Mar. 31, 2019
Debt, Weighted Average Interest Rate	5.03%		4.99%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	69.00%		66.00%
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	$ 24,900
Bank Credit Facility	275,000		$ 387,061
Letters of Credit Outstanding, Amount	$ 32,900
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Line of Credit Facility, Remaining Borrowing Capacity	$ 692,100
Repayments of Long-term Debt	8,535	$ 8,535
Gain (Loss) on Extinguishment of Debt	0	(10,131)
Repayments of Debt	143,500	268,100
Repayments of Long-term Capital Lease Obligations	10,657	7,646
December 2022
Debt Instrument [Line Items]
Bank Credit Facility	275,000
Term Loan	632,813		641,250
Letters of Credit Outstanding, Amount			395,000
Redemption Premium		9,600
Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net		10,000
Repayments of Debt	8,400
October 2018
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net		175,000
Repayments of Long-term Debt		$ 250,000
Bank Credit Facility due March 2022 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net	15,000
Repayments of Debt	135,000
Other Debt [Member]
Debt Instrument [Line Items]
Repayments of Debt	100
Unsecured Debt | May 2024
Debt Instrument [Line Items]
Senior Notes	$ 850,000		$ 850,000