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Debt (Summary of Debt) (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Feb. 28, 2025 | Dec. 31, 2024 | Sep. 30, 2024 | Dec. 31, 2023 | Dec. 19, 2023 | Mar. 07, 2019
--- | --- | --- | --- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Revolving secured line of credit balance outstanding |  | $ 148.7 |  | $ 0.1 |  |  |  |
Secured Debt |  | 5,133.1 |  | 5,361.5 |  |  |  |
Senior notes balance outstanding |  | 1,087.2 |  | 991.3 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | 482.9 |  | 501.3 | $ 556.6 | $ 457.7 |  |
Revolving Secured Line of Credit [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Revolving secured line of credit balance outstanding |  | 148.7 |  | 0.1 |  |  |  |
Amount available for borrowing | [1] | $ 261.3 |  | $ 409.9 |  |  |  |
Line of credit facility, interest rate |  | 6.14% |  | 6.37% |  |  |  |
Warehouse Facility II [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 0.0 |  | $ 0.0 |  |  |  |
Amount available for borrowing | [1] | 500.0 |  | 500.0 |  |  |  |
Loans pledged as collateral |  | 0.0 |  | 0.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 0.0 |  | $ 2.5 |  |  |  |
Interest rate |  | 0.00% |  | 0.00% |  |  |  |
Warehouse Facility IV [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 0.0 |  | $ 0.0 |  |  |  |
Amount available for borrowing | [1] | 300.0 |  | 300.0 |  |  |  |
Loans pledged as collateral |  | 0.0 |  | 0.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 0.0 |  | $ 0.0 |  |  |  |
Interest rate |  | 0.00% |  | 0.00% |  |  |  |
Warehouse Facility V [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 0.0 |  | $ 0.0 |  |  |  |
Amount available for borrowing | [1] | 250.0 |  | 250.0 |  |  |  |
Loans pledged as collateral |  | 0.0 |  | 0.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 1.0 |  | $ 1.0 |  |  |  |
Interest rate |  | 0.00% |  | 0.00% |  |  |  |
Warehouse Facility VI [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 0.0 |  | $ 0.0 |  |  |  |
Amount available for borrowing | [1] | 75.0 |  | 75.0 |  |  |  |
Loans pledged as collateral |  | 0.0 |  | 0.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 0.0 |  | $ 0.0 |  |  |  |
Interest rate |  | 0.00% |  | 0.00% |  |  |  |
Warehouse Facility VIII [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 0.0 |  | $ 0.0 |  |  |  |
Amount available for borrowing | [1] | 200.0 |  | 200.0 |  |  |  |
Loans pledged as collateral |  | 0.0 |  | 0.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 0.0 |  | $ 0.0 |  |  |  |
Interest rate |  | 0.00% |  | 0.00% |  |  |  |
Term ABS 2019-2 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 500.0 |  | $ 500.0 |  |  |  |
Loans pledged as collateral |  | 530.0 |  | 529.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 43.1 |  | $ 41.7 |  |  |  |
Interest rate |  | 5.43% |  | 5.43% |  |  |  |
Term ABS 2021-1 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 100.0 |  | $ 100.0 |  |  |  |
Loans pledged as collateral |  | 108.1 |  | 112.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 9.0 |  | $ 8.7 |  |  |  |
Interest rate |  | 6.35% |  | 6.60% |  |  |  |
Term ABS 2021-4 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 0.0 |  | $ 63.6 |  |  |  |
Loans pledged as collateral |  | 0.0 |  | 167.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 0.0 |  | $ 16.4 |  |  |  |
Interest rate |  | 0.00% |  | 1.89% |  |  |  |
Term ABS 2022-1 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 86.5 |  | $ 236.6 |  |  |  |
Loans pledged as collateral |  | 213.4 |  | 310.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 21.7 |  | $ 24.9 |  |  |  |
Interest rate |  | 5.92% |  | 5.24% |  |  |  |
Term ABS 2022-2 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 300.0 |  | $ 300.0 |  |  |  |
Loans pledged as collateral |  | 325.4 |  | 406.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 24.5 |  | $ 25.2 |  |  |  |
Interest rate |  | 6.58% |  | 7.29% |  |  |  |
Term ABS 2022-3 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 175.2 |  | $ 347.6 |  |  |  |
Loans pledged as collateral |  | 272.1 |  | 395.2 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 25.8 |  | $ 29.1 |  |  |  |
Interest rate |  | 8.70% |  | 7.82% |  |  |  |
Term ABS 2023-1 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 266.6 |  | $ 400.0 |  |  |  |
Loans pledged as collateral |  | 331.4 |  | 453.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 29.7 |  | $ 33.1 |  |  |  |
Interest rate |  | 7.14% |  | 6.92% |  |  |  |
Term ABS 2023-2 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 306.2 |  | $ 400.0 |  |  |  |
Loans pledged as collateral |  | 380.4 |  | 533.3 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 32.7 |  | $ 36.8 |  |  |  |
Interest rate |  | 6.53% |  | 6.39% |  |  |  |
Term ABS 2023-3 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 377.0 |  | $ 400.0 |  |  |  |
Loans pledged as collateral |  | 413.3 |  | 524.9 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 33.5 |  | $ 36.5 |  |  |  |
Interest rate |  | 6.88% |  | 6.86% |  |  |  |
Term ABS 2023-A [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 200.0 |  | $ 200.0 |  |  |  |
Loans pledged as collateral |  | 216.9 |  | 252.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 16.9 |  | $ 17.7 |  |  |  |
Interest rate |  | 7.51% |  | 7.51% |  |  |  |
Term ABS 2023-5 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 294.0 |  | $ 294.0 |  |  |  |
Loans pledged as collateral |  | 326.6 |  | 398.7 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 30.5 |  | $ 32.9 |  |  |  |
Interest rate |  | 6.54% |  | 6.54% |  |  |  |
Term ABS 2024-A [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 200.0 |  | $ 200.0 |  |  |  |
Loans pledged as collateral |  | 211.7 |  | 248.4 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 16.7 |  | $ 18.1 |  |  |  |
Interest rate |  | 7.45% |  | 7.45% |  |  |  |
Term ABS 2024-1 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 500.0 |  | $ 500.0 |  |  |  |
Loans pledged as collateral |  | 582.2 |  | 553.3 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 46.8 |  | $ 45.0 |  |  |  |
Interest rate |  | 6.01% |  | 6.01% |  |  |  |
Term ABS 2024-2 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 550.0 |  | $ 550.0 |  |  |  |
Loans pledged as collateral |  | 607.5 |  | 646.8 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 44.5 |  | $ 42.0 |  |  |  |
Interest rate |  | 6.21% |  | 6.21% |  |  |  |
Term ABS 2024-3 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 600.0 |  | $ 600.0 |  |  |  |
Loans pledged as collateral |  | 665.9 |  | 700.9 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 49.9 |  | $ 51.5 |  |  |  |
Interest rate |  | 4.91% |  | 4.91% |  |  |  |
Term ABS 2024-B [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 300.0 |  | $ 300.0 |  |  |  |
Loans pledged as collateral |  | 341.7 |  | 425.8 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 23.5 |  | $ 37.9 |  |  |  |
Interest rate |  | 6.13% |  | 6.13% |  |  |  |
Term ABS 2025-1 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Secured Debt |  | $ 400.0 |  |  |  |  |  |
Loans pledged as collateral |  | 470.9 |  | $ 0.0 |  |  |  |
Restricted cash and cash equivalents pledged as collateral |  | $ 32.8 |  |  |  |  |  |
Interest rate |  | 5.26% |  |  |  |  |  |
2026 Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Senior notes balance outstanding |  | $ 0.0 |  | $ 400.0 |  |  |  |
Interest rate |  | 0.00% |  | 6.625% |  |  |  | 6.625%
2028 Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Senior notes balance outstanding |  | $ 600.0 |  | $ 600.0 |  |  |  |
Interest rate |  | 9.25% |  | 9.25% |  |  | 9.25% |
2030 Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Senior notes balance outstanding |  | $ 500.0 |  | $ 0.0 |  |  |  |
Interest rate |  | 6.625% | 6.625% | 0.00% |  |  |  |
[1] | Availability may be limited by the amount of assets pledged as collateral.

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -SubTopic 10 -Topic 210 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
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