Debt (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended
		Mar. 07, 2019	Mar. 31, 2024		Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2023	Dec. 18, 2019	Aug. 06, 2018
Debt Instrument [Line Items]
Maximum hedging reserve			$ 1.0
Unamortized Debt Issuance Costs			$ (38.6)				$ (36.6)
Percentage of collections on newer contributed loans			4.00%
Percentage of collections on contributed loans			6.00%
Monthly servicing fee per financing			6.00%
Monthly servicing fee per newer financings			4.00%
Mortgage note	[1]		$ 8.3				8.4
Repayment of senior notes						$ 322.3
Senior notes			989.6				989.0
Loss on extinguishment of debt						$ 1.8
Carrying Amount			5,611.5				5,067.5
Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs			(10.4)				(11.0)
Carrying Amount			989.6				989.0
Mortgages [Member]
Debt Instrument [Line Items]
Debt facility financing amount			9.0	[2]					$ 9.0
Unamortized Debt Issuance Costs			0.0				0.0
Mortgage note			$ 8.3				$ 8.4
Debt maturity date	[2]		Aug. 06, 2028
Senior notes yield to maturity			6.87%				6.88%
Carrying Amount			$ 8.3				$ 8.4
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility			$ 390.0
Percentage of net book value of loans			80.00%
Unamortized Debt Issuance Costs	[3]		$ 0.0				0.0
Carrying Amount	[3]		$ 169.5				$ 79.2
Warehouse Facilities [Member]
Debt Instrument [Line Items]
Percentage of net book value of loans			80.00%
Number of warehouse facilities			5
Debt facility financing amount			$ 1,175.0
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]		$ 400.0
Debt maturity date	[2],[4]		Apr. 30, 2026
Senior notes yield to maturity			0.00%				0.00%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]		$ 300.0
Debt maturity date	[2],[4]		Dec. 29, 2026
Senior notes yield to maturity			0.00%				0.00%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]		$ 200.0
Debt maturity date	[2],[5]		Dec. 29, 2025
Senior notes yield to maturity			0.00%				0.00%
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]		$ 75.0
Debt maturity date	[2],[4]		Sep. 30, 2026
Senior notes yield to maturity			7.37%				0.00%
Term ABS 2019-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]		$ 500.0
Debt financing close date			Aug. 28, 2019
Debt maturity date	[2],[6]		Aug. 15, 2025
Senior notes yield to maturity			5.15%				5.15%
Net Book Value Of Loans Pledged As Collateral			$ 625.1
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount								$ 400.0
Repayment of senior notes					$ 77.7
Senior notes yield to maturity								5.125%
2024 Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes								$ 600.0
Senior notes yield to maturity								9.25%
2026 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount		$ 400.0	$ 400.0
Close date, secured financings		Mar. 07, 2019
Senior notes stated interest rate		6.625%
Debt maturity date		Mar. 15, 2026	Mar. 15, 2026
Senior notes			$ 400.0				$ 400.0
Senior notes yield to maturity			6.625%				6.625%
Term ABS 2021-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]		$ 500.0
Debt financing close date			Feb. 18, 2021
Debt maturity date	[2],[4]		Feb. 15, 2023
Senior notes yield to maturity			1.58%				1.38%
Net Book Value Of Loans Pledged As Collateral			$ 625.1

[1] Measured at amortized cost with fair value disclosed.

[2] Financing made available only to a specified subsidiary of the Company.

[3] Excludes deferred debt issuance costs of $3.8 million and $4.2 million as of March 31, 2024 and December 31, 2023, respectively, which are included in other assets.

[4] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date based on the cash flows of the pledged assets.

[5] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on December 27, 2027 will be due on that date.

[6] Represents the revolving maturity date. The Company has the option to redeem and retire the indebtedness after the revolving maturity date. If we do not elect this option, the outstanding balance will amortize based on the cash flows of the pledged assets