Auto Loans Receivable - Financing Receivable Credit Quality Indicators (Details) $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($) fICOScore	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) fICOScore
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 1,206.2		$ 932.0
Auto loans receivable, Originated in year before current year	698.8		141.8
Auto loans receivable, Originated two years before current year	100.4		4.5
Auto loans receivable, Originated three years before current year	2.7		20.6
Auto loans receivable, Originated four years before current year	10.1		4.6
Auto loans receivable, Originated five years or more before current year	1.8		0.3
Total auto loans receivable	2,020.0		1,103.8
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current-period gross write-offs, 2025 origination	8.3
Current-period gross write-offs, 2024 origination	30.0
Current-period gross write-offs, 2023 origination	12.2
Current-period gross write-offs, 2022 origination	1.1
Current-period gross write-offs, 2021 origination	2.7
Current-period gross write-offs, Prior to 2021 origination	0.5
Current-period gross write-offs	54.8	$ 44.6
Palladium
Auto Loans Receivable
Auto loans receivable, Originated in current year	490.6		194.0
Auto loans receivable, Originated in year before current year	140.8		0.0
Auto loans receivable, Originated two years before current year	0.0		0.0
Auto loans receivable, Originated three years before current year	0.0		0.0
Auto loans receivable, Originated four years before current year	0.0		0.0
Auto loans receivable, Originated five years or more before current year	0.0		0.0
Total auto loans receivable	$ 631.4		$ 194.0
Palladium | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	732		734
Rhodium
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 236.6		$ 147.6
Auto loans receivable, Originated in year before current year	109.4		16.9
Auto loans receivable, Originated two years before current year	12.2		0.1
Auto loans receivable, Originated three years before current year	0.1		0.0
Auto loans receivable, Originated four years before current year	0.0		0.0
Auto loans receivable, Originated five years or more before current year	0.0		0.0
Total auto loans receivable	$ 358.3		$ 164.6
Rhodium | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	698		702
Platinum
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 454.9		$ 525.1
Auto loans receivable, Originated in year before current year	399.2		82.3
Auto loans receivable, Originated two years before current year	59.1		1.7
Auto loans receivable, Originated three years before current year	1.1		4.0
Auto loans receivable, Originated four years before current year	2.2		1.0
Auto loans receivable, Originated five years or more before current year	0.5		0.1
Total auto loans receivable	$ 917.0		$ 614.2
Platinum | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	652		651
Gold
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 21.2		$ 64.9
Auto loans receivable, Originated in year before current year	49.1		25.0
Auto loans receivable, Originated two years before current year	17.2		1.3
Auto loans receivable, Originated three years before current year	0.7		7.3
Auto loans receivable, Originated four years before current year	4.0		1.6
Auto loans receivable, Originated five years or more before current year	0.7		0.1
Total auto loans receivable	$ 92.9		$ 100.2
Gold | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	624		623
Silver
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 1.9		$ 0.3
Auto loans receivable, Originated in year before current year	0.2		13.4
Auto loans receivable, Originated two years before current year	9.1		1.2
Auto loans receivable, Originated three years before current year	0.6		5.4
Auto loans receivable, Originated four years before current year	2.4		1.2
Auto loans receivable, Originated five years or more before current year	0.4		0.1
Total auto loans receivable	$ 14.6		$ 21.6
Silver | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	574		574
Bronze
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 0.8		$ 0.1
Auto loans receivable, Originated in year before current year	0.1		4.0
Auto loans receivable, Originated two years before current year	2.7		0.2
Auto loans receivable, Originated three years before current year	0.2		2.8
Auto loans receivable, Originated four years before current year	1.2		0.6
Auto loans receivable, Originated five years or more before current year	0.2		0.0
Total auto loans receivable	$ 5.2		$ 7.7
Bronze | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	547		551
Copper
Auto Loans Receivable
Auto loans receivable, Originated in current year	$ 0.2		$ 0.0
Auto loans receivable, Originated in year before current year	0.0		0.2
Auto loans receivable, Originated two years before current year	0.1		0.0
Auto loans receivable, Originated three years before current year	0.0		1.1
Auto loans receivable, Originated four years before current year	0.3		0.2
Auto loans receivable, Originated five years or more before current year	0.0		0.0
Total auto loans receivable	$ 0.6		$ 1.5
Copper | Weighted Average
Auto Loans Receivable
Auto loans receivable, FICO Score | fICOScore	558		562