Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Total revenue	$ 119.9	$ 105.7
Segment economic net income	31.9	22.9
Unallocated corporate expenses	(4.5)	(4.6)
Adjustments and reconciling items	1.2	0.5
Non-cash compensation expenses for Acadian LLC key employee equity and profit interest revaluations	0.3	(4.4)
Investment income	0.3	0.9
Interest income	1.1	1.3
Interest expense	(4.8)	(5.0)
Income before income taxes	32.1	21.8
Income tax expense	(8.3)	(6.1)
Net income	23.8	15.7
Net income attributable to redeemable non-controlling interests in consolidated Funds	(3.7)	(1.1)
Net income attributable to controlling interests	20.1	14.6
Hold Co
Segment Reporting Information [Line Items]
Fixed compensation and benefits	2.4	2.5
General and administrative expense	2.1	2.1
Consolidated Funds
Segment Reporting Information [Line Items]
Total revenue	1.7	0.4
Net consolidated Funds' investment gains	3.6	1.7
Consolidated Entity Excluding Consolidated Funds
Segment Reporting Information [Line Items]
Fixed compensation and benefits	60.8	58.1
Depreciation and amortization	4.2	4.6
Investment income	0.3	0.9
Interest income	1.1	1.3
Interest expense	(4.8)	(5.0)
Net income	23.8	15.7
Quant And Solutions
Segment Reporting Information [Line Items]
Fixed compensation and benefits	22.9	21.6
Variable compensation	29.4	26.0
Acadian LLC key employee distributions	3.1	2.2
Depreciation and amortization	4.2	4.6
Other segment items	23.7	19.5
Segment economic net income	34.9	31.4
Income before income taxes	32.1	21.8
Income tax expense	(8.3)	(6.1)
Net income	23.8	15.7
Net income attributable to redeemable non-controlling interests in consolidated Funds	(3.7)	(1.1)
Net income attributable to controlling interests	20.1	14.6
Quant And Solutions | Consolidated Entity Excluding Consolidated Funds
Segment Reporting Information [Line Items]
Total revenue	$ 118.2	$ 105.3