Lines of Credit and Financing Arrangements (Details Textual 1) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Nov. 30, 2014	Oct. 31, 2013	Nov. 13, 2014	Nov. 12, 2014
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	0.79%		0.79%
Percent of maximum available amount used to charge unused fee	101.00%
Fixed rate of agreement	0.30%
Unused fee	$ 0.0005
Maximum [Member]
Line of Credit Facility [Line Items]
Maximum securitization, amount				220,000,000	220,000,000
Minimum [Member]
Line of Credit Facility [Line Items]
Maximum securitization, amount				180,000,000	160,000,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Restrictive Covenants	75,000,000
Domestic Credit Facility [Member]
Line of Credit Facility [Line Items]
Domestic Revolving Credit Facility						950,000,000
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	950,000,000					650,000,000	650,000,000
Borrowings under Domestic Revolving Credit Facility	683,500,000
Committed standby letters of credit	27,200,000
Available for future borrowings	239,300,000
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	300,000,000					300,000,000
Periodic payments	$ 7,500,000