Borrowings and Debt - Schedule of Long Term Debt (Details) - USD ($) $ in Millions		12 Months Ended
	Dec. 01, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Oct. 28, 2025	Oct. 27, 2025
Debt Instrument [Line Items]
Carrying value		$ 200.0
Loss on extinguishment of debt		1.4	$ 0.0	$ 0.0
Third-Party Borrowings
Debt Instrument [Line Items]
Carrying value		200.0	274.3
Fair Value		200.0	271.7
4.80% Senior Notes Due July 27, 2026 | Senior notes
Debt Instrument [Line Items]
Face amount		$ 275.0
Interest rate		4.80%
Carrying value		$ 0.0	274.3
Fair Value		0.0	271.7
Repayments of senior debt	$ 275.0
Loss on extinguishment of debt		1.4
Revolving credit facility | Line of Credit
Debt Instrument [Line Items]
Carrying value		0.0	0.0
Fair Value		0.0	0.0
Revolving credit facility | The Acadian Credit Agreement | Line of Credit
Debt Instrument [Line Items]
Face amount		140.0
Carrying value		0.0	0.0
Fair Value		$ 0.0	$ 0.0
Maximum borrowing capacity						$ 140.0
Weighted average interest rate		5.93%	6.93%	6.19%
Revolving credit facility | Revolving Credit Agreement | Line of Credit
Debt Instrument [Line Items]
Face amount		$ 175.0
Carrying value		0.0	$ 0.0
Fair Value		0.0	0.0
Maximum borrowing capacity					$ 175.0
Secured Debt | DDTL Credit Agreement | Line of Credit
Debt Instrument [Line Items]
Face amount		200.0			$ 200.0
Carrying value		200.0	0.0
Fair Value		$ 200.0	$ 0.0
Weighted average interest rate		5.65%