Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Flows From Operating Activities:
Net income	$ 219.7	$ 188.0	$ 170.1
Adjustments to reconcile cash provided by operating activities:
Provision for credit losses	24.0	29.0	10.0
Depreciation	5.1	4.1	4.4
Amortization	7.1	5.9	6.6
Loss on retirement of property and equipment			0.1
Loss on impairment of software			1.4
Provision for deferred income taxes	25.0	15.3	13.9
Stock-based compensation	12.2	1.9	4.1
Change in operating assets and liabilities:
Increase (decrease) in accounts payable and accrued liabilities	10.0	20.7	(0.7)
(Increase) decrease in income taxes receivable	(0.6)	11.5	(8.1)
Increase in income taxes payable	4.8	1.5
Decrease (increase) in other assets	1.3	(2.2)	(1.1)
Net cash provided by operating activities	308.6	275.7	200.7
Cash Flows From Investing Activities:
Decrease (increase) in restricted cash and cash equivalents	12.3	(38.1)	15.9
Purchases of restricted securities available for sale	(57.1)	(0.5)	(1.1)
Proceeds from sale of restricted securities available for sale	2.0	0.1	2.1
Maturities of restricted securities available for sale	9.6	0.4	1.3
Principal collected on Loans receivable	1,162.8	996.9	785.9
Advances to Dealers	(1,253.6)	(1,152.5)	(786.9)
Purchases of Consumer Loans	(108.8)	(122.2)	(100.4)
Accelerated payments of Dealer Holdback	(43.7)	(47.4)	(32.6)
Payments of Dealer Holdback	(115.7)	(85.2)	(44.2)
Net decrease in other loans	0.1	0.8	0.2
Purchases of property and equipment	(8.8)	(6.3)	(3.5)
Net cash used in investing activities	(400.9)	(454.0)	(163.3)
Cash Flows From Financing Activities:
Borrowings under revolving secured line of credit	2,507.4	2,384.9	1,097.9
Repayments under revolving secured line of credit	(2,507.8)	(2,477.7)	(1,058.5)
Proceeds from secured financing	1,742.0	1,164.5	327.7
Repayments of secured financing	(1,488.3)	(865.3)	(432.2)
Principal payments under mortgage note and capital lease obligations	(0.3)	(0.3)	(0.5)
Proceeds from sale of senior notes		106.0	243.7
Payments of debt issuance costs	(6.5)	(8.4)	(15.2)
Repurchase of common stock	(152.5)	(130.8)	(202.2)
Proceeds from stock options exercised	0.6	2.9	2.9
Tax benefits from stock-based compensation plans	2.0	3.4	0.6
Net cash provided by (used in) financing activities	96.6	179.2	(35.8)
Net increase in cash and cash equivalents	4.3	0.9	1.6
Cash and cash equivalents, beginning of period	4.7	3.8	2.2
Cash and cash equivalents, end of period	9.0	4.7	3.8
Supplemental Disclosure of Cash Flow Information:
Cash paid during the period for interest	56.2	51.4	42.5
Cash paid during the period for income taxes	$ 92.4	$ 76.5	$ 81.8