Lines of Credit and Financing Arrangements (Details Textual 1)	1 Months Ended	9 Months Ended
	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014	Nov. 30, 2014 USD ($)	Nov. 13, 2014 USD ($)	Nov. 12, 2014 USD ($)
Line of Credit Facility [Line Items]
Maximum securitization as percentage of net pool balance		100.00%
Program fee		0.60%
Average floating commercial paper rate		0.82%	0.79%
Unused fee		101.00%
Fixed rate of agreement		0.30%
Unused fee charged on incremental available amounts		$ 0.0005
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowings under Domestic Revolving Credit Facility		475,500,000
Committed standby letters of credit		4,400,000
Available for future borrowings		447,600,000
Maximum [Member]
Line of Credit Facility [Line Items]
Maximum securitization, amount		220,000,000
Minimum [Member]
Line of Credit Facility [Line Items]
Maximum securitization, amount		180,000,000		$ 180,000,000
Domestic Credit Facility [Member]
Line of Credit Facility [Line Items]
Domestic Revolving Credit Facility					$ 950,000,000
Domestic Credit Facility [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum increase in borrowings under Domestic Revolving Credit Facility		$ 350,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Domestic Revolving Credit Facility					650,000,000	$ 650,000,000
Revolving Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Indebtedness to adjusted EBITDA ratio		3.5
Revolving Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Cash flow to net interest expense ratio		3.0
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Domestic Revolving Credit Facility		$ 150,000,000
Subfacility for Swingline Loans [Member]
Line of Credit Facility [Line Items]
Domestic Revolving Credit Facility		65,000,000
Medium-term Notes [Member] | Domestic Credit Facility [Member]
Line of Credit Facility [Line Items]
Face amount of debt		278,000,000			$ 300,000,000
Periodic payments	$ 22,500,000	$ 7,500,000