Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash Flows From Operating Activities:
Net income	$ 187.2	$ 159.8
Adjustments to reconcile cash provided by operating activities:
Provision for credit losses	17.3	17.8
Depreciation	4.1	3.7
Amortization	5.5	5.1
Loss on retirement of property and equipment	0.1
(Benefit) provision for deferred income taxes	(2.6)	11.9
Stock-based compensation	6.0	8.6
Change in operating assets and liabilities:
Increase in accounts payable and accrued liabilities	4.1	2.3
(Increase) decrease in income taxes receivable	(0.1)	0.5
(Decrease) increase in income taxes payable	(0.6)	8.5
Decrease in other assets	0.4	0.3
Net cash provided by operating activities	221.4	218.5
Cash Flows From Investing Activities:
Increase in restricted cash and cash equivalents	(23.8)	(63.0)
Purchases of restricted securities available for sale	(75.4)	(0.1)
Proceeds from sale of restricted securities available for sale	9.6	0.9
Maturities of restricted securities available for sale	59.7
Principal collected on Loans receivable	1,008.4	882.6
Advances to Dealers	(1,048.0)	(968.7)
Purchases of Consumer Loans	(90.2)	(86.0)
Accelerated payments of Dealer Holdback	(30.8)	(34.1)
Payments of Dealer Holdback	(86.3)	(89.7)
Net increase in other loans	(0.3)
Purchases of property and equipment	(4.3)	(7.1)
Net cash used in investing activities	(281.4)	(365.2)
Cash Flows From Financing Activities:
Borrowings under revolving secured line of credit	2,068.1	1,969.7
Repayments under revolving secured line of credit	(2,024.0)	(1,897.8)
Proceeds from secured financing	806.9	1,426.7
Repayments of secured financing	(667.5)	(1,234.1)
Principal payments under mortgage note	(0.2)	(0.2)
Payments of debt issuance costs	(3.5)	(6.0)
Repurchase of common stock	(127.2)	(113.0)
Proceeds from stock options exercised	0.6	0.5
Tax benefits from stock-based compensation plans	1.4	1.9
Net cash provided by financing activities	54.6	147.7
Net (decrease) increase in cash and cash equivalents	(5.4)	1.0
Cash and cash equivalents, beginning of period	9.0	4.7
Cash and cash equivalents, end of period	3.6	5.7
Supplemental Disclosure of Cash Flow Information:
Cash paid during the period for interest	51.0	49.8
Cash paid during the period for income taxes	$ 108.3	$ 68.9