Debt Debt, Textuals (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2016
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.68%	5.18%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	63.00%	76.00%
Notes Payable to Bank, Noncurrent	$ 0	$ 310,000
Proceeds from Issuance of Long-term Debt	$ 300,000
Line of Credit Facility, Amount Outstanding		500,000		$ 500,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.30%
Letters of Credit, Maximum Borrowing Capacity	$ 32,700	175,000		100,000
Line of Credit Facility, Remaining Borrowing Capacity	317,300
Principal payments on capital leases	33,119	28,601	$ 29,380
Repayments of Other Debt	200	200
Repayments of Debt		357,600
Losses on early extinguishment of debt, net	(22,503)	(6,918)	(29,158)
Debt Instrument, Unamortized Premium	11,300
Capital Lease Obligations Incurred	41,609	55,941	$ 35,422
Pledged Assets Separately Reported, Finance Receivables Pledged as Collateral, at Fair Value	4,700	7,000
Pledged Assets, Other, Not Separately Reported on Statement of Financial Position	1,400	1,500
Long-term Debt, Fair Value	3,240,560	3,101,760
Bank Credit Agreement				1,400,000
Term Loan, Maximum Borrowing Capacity				600,000
Debt Issuance Costs, Line of Credit Arrangements, Net	5,200
July 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	0	270,000
Repayments of Debt	310,000	60,000
April 2016 [Member]
Debt Instrument [Line Items]
Repayments of Debt		197,400
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Repayments of Debt	280,000	100,000
June 2017 [Member]
Debt Instrument [Line Items]
Repayments of Debt	295,000
March 2021 [Member]
Debt Instrument [Line Items]
Notes Payable to Bank, Noncurrent	673,750	0
Proceeds from Issuance of Long-term Debt	700,000
Line of Credit Facility, Amount Outstanding	350,000	0
Repayments of Debt	26,300
Bank Credit Facility due March 2021 [Domain]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 700,000
Proceeds from Issuance of Long-term Debt	360,000
Line of Credit Facility, Amount Outstanding	350,000	0
Unsecured Debt [Member] | July 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	0	270,000
Unsecured Debt [Member] | June 2017 [Member]
Debt Instrument [Line Items]
Senior Notes	0	295,000
Unsecured Debt [Member] | October 2018 [Member]
Debt Instrument [Line Items]
Senior Notes	250,000	250,000
Unsecured Debt [Member] | May 2019 [Member]
Debt Instrument [Line Items]
Senior Notes	200,000	200,000
Unsecured Debt [Member] | November 2021 [Member]
Debt Instrument [Line Items]
Senior Notes	150,000	150,000
Unsecured Debt [Member] | April 2027 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 200,000	$ 200,000