Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash Flows From Operating Activities:
Net income	$ 286.1	$ 535.8	$ 958.3
Adjustments to reconcile cash provided by operating activities:
Provision for credit losses	736.2	481.4	8.4
Depreciation	8.9	9.0	9.7
Amortization	17.7	16.6	16.6
Increase (Decrease) in Deferred Income Taxes	(38.0)	(7.7)	44.7
Stock-based compensation	39.1	36.5	24.8
Loss on extinguishment of debt	1.8	0.0	0.0
Other Operating Activities, Cash Flow Statement	0.6	0.3	(0.4)
Change in operating assets and liabilities:
Increase in accounts payable and accrued liabilities	49.7	67.9	(10.7)
Increase in income taxes receivable	4.4	100.5	37.8
Increase (decrease) in income taxes payable	78.5	2.3	0.0
Increase in other assets	18.8	(3.9)	(19.8)
Net cash provided by operating activities	1,203.8	1,238.7	1,069.4
Cash Flows From Investing Activities:
Purchases of restricted securities available for sale	(43.3)	(50.1)	(38.8)
Proceeds from Sale of Debt Securities, Available-for-sale	15.8	11.1	22.2
Maturities of restricted securities available for sale	8.5	24.3	18.3
Principal collected on Loans receivable	3,036.8	3,413.3	3,808.5
Advances to Dealers	(2,933.7)	(2,530.0)	(2,059.0)
Purchases of Consumer Loans	(1,214.1)	(1,095.3)	(1,108.8)
Accelerated payments of Dealer Holdback	(46.9)	(44.2)	(44.1)
Payments of Dealer Holdback	(235.9)	(186.6)	(153.4)
Purchases of property and equipment	(4.0)	(3.1)	(7.6)
Net cash used in investing activities	(1,416.8)	(460.6)	437.3
Cash Flows From Financing Activities:
Borrowings under revolving secured line of credit	7,431.9	6,622.6	1,562.6
Repayments under revolving secured line of credit	(7,383.6)	(6,594.3)	(1,655.9)
Proceeds from secured financing	2,762.0	1,541.9	1,830.8
Repayments of secured financing	(2,519.8)	(1,599.2)	(1,729.0)
Proceeds from issuance of senior notes	600.0	0.0	0.0
Repayments of senior notes	(400.0)	0.0	0.0
Payments of debt issuance costs and debt issuance costs	(33.3)	(12.5)	(16.4)
Repurchase of common stock	(202.6)	(784.5)	(1,471.8)
Proceeds from Issuance of Common Stock	5.2	15.1	11.8
Other financing activities	6.4	16.3	(0.8)
Net cash provided by financing activities	266.2	(794.6)	(1,468.7)
Net increase in cash and cash equivalents and restricted cash and cash equivalents	53.2	(16.5)	38.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	417.7	434.2	396.2
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	470.9	417.7	434.2
Supplemental Cash Flow Information [Abstract]
Cash paid during the period for interest	242.1	147.3	149.4
Cash paid during the period for income taxes	$ 31.9	$ 72.7	$ 213.2