Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows From Operating Activities:
Net income	$ 958.3	$ 421.0	$ 656.1
Adjustments to reconcile cash provided by operating activities:
Provision for credit losses	8.4	556.9	76.4
Depreciation	9.7	8.8	7.3
Amortization	16.6	15.0	15.1
Increase (Decrease) in Deferred Income Taxes	44.7	68.3	85.5
Stock-based compensation	24.8	6.2	7.6
Loss on extinguishment of debt	0.0	7.4	1.8
Other Operating Activities, Cash Flow Statement	(0.4)	(0.7)	(0.2)
Change in operating assets and liabilities:
Increase in accounts payable and accrued liabilities	(10.7)	(18.4)	17.3
Increase in income taxes receivable	37.8	(80.8)	(58.3)
Increase (decrease) in income taxes payable	0.0	0.0	(2.3)
Increase in other assets	(19.8)	1.5	6.0
Net cash provided by operating activities	1,069.4	985.2	812.3
Cash Flows From Investing Activities:
Purchases of restricted securities available for sale	(38.8)	(43.2)	(40.1)
Proceeds from Sale of Debt Securities, Available-for-sale	22.2	24.8	29.1
Maturities of restricted securities available for sale	18.3	13.0	11.9
Principal collected on Loans receivable	3,808.5	3,170.1	2,971.2
Advances to Dealers	(2,059.0)	(2,207.8)	(2,424.5)
Purchases of Consumer Loans	(1,108.8)	(1,433.4)	(1,347.7)
Accelerated payments of Dealer Holdback	(44.1)	(45.9)	(58.8)
Payments of Dealer Holdback	(153.4)	(142.6)	(138.5)
Purchases of property and equipment	(7.6)	(8.5)	(26.8)
Net cash used in investing activities	437.3	(673.5)	(1,024.2)
Cash Flows From Financing Activities:
Borrowings under revolving secured line of credit	1,562.6	5,376.0	3,846.7
Repayments under revolving secured line of credit	(1,655.9)	(5,280.1)	(4,018.6)
Proceeds from secured financing	1,830.8	2,800.2	2,396.4
Repayments of secured financing	(1,729.0)	(2,427.2)	(2,149.5)
Proceeds from issuance of senior notes	0.0	0.0	800.0
Repayments of senior notes	0.0	(401.8)	(148.2)
Payments of debt issuance costs and debt issuance costs	(16.4)	(18.7)	(25.5)
Repurchase of common stock	(1,471.8)	(480.8)	(300.4)
Proceeds from Issuance of Common Stock	11.8	0.0	0.0
Other financing activities	(0.8)	(0.8)	(0.6)
Net cash provided by financing activities	(1,468.7)	(433.2)	400.3
Net increase in cash and cash equivalents and restricted cash and cash equivalents	38.0	(121.5)	188.4
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	396.2	517.7	329.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	434.2	396.2	517.7
Supplemental Cash Flow Information [Abstract]
Cash paid during the period for interest	149.4	191.6	175.6
Cash paid during the period for income taxes	$ 213.2	$ 141.5	$ 172.4