Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting Information [Line Items]
Total revenue	$ 127.4	$ 109.0	$ 247.3	$ 214.7
Segment economic net income	16.2	20.6	48.1	43.5
Unallocated corporate expenses	(4.8)	(4.8)	(9.3)	(9.4)
Adjustments and reconciling items	1.4	(0.4)	2.6	0.1
Non-cash compensation expenses for Acadian LLC key employee equity and profit interest revaluations	(19.7)	(5.9)	(19.4)	(10.3)
Investment income (loss)	(0.2)	0.1	0.1	1.0
Interest income	0.8	0.9	1.9	2.2
Interest expense	(5.3)	(5.3)	(10.1)	(10.3)
Income before income taxes	23.6	17.1	55.7	38.9
Income tax expense	(4.5)	(5.6)	(12.8)	(11.7)
Net income	19.1	11.5	42.9	27.2
Net income attributable to controlling interests	10.1	11.0	30.2	25.6
Hold Co
Segment Reporting Information [Line Items]
Fixed compensation and benefits	2.6	2.3	5.0	4.8
General and administrative expense	2.2	2.5	4.3	4.6
Consolidated Funds
Segment Reporting Information [Line Items]
Total revenue	2.5	0.7	4.2	1.1
Net consolidated Funds' investment gains	12.1	0.8	15.7	2.5
Consolidated Entity Excluding Consolidated Funds
Segment Reporting Information [Line Items]
Fixed compensation and benefits	83.8	62.2	144.6	120.3
Depreciation and amortization	4.2	5.0	8.4	9.6
Investment income (loss)	(0.2)	0.1	0.1	1.0
Interest income	0.8	0.9	1.9	2.2
Interest expense	(5.3)	(5.3)	(10.1)	(10.3)
Net income			42.9	27.2
Quant And Solutions
Segment Reporting Information [Line Items]
Fixed compensation and benefits	23.4	22.6	46.3	44.2
Variable compensation	30.8	26.8	60.2	52.8
Acadian LLC key employee distributions	4.0	2.1	7.1	4.3
Depreciation and amortization	4.2	4.6	8.4	9.2
Other segment items	23.2	20.5	46.9	40.0
Segment economic net income	39.3	31.7	74.2	63.1
Income before income taxes	23.6	17.1	55.7	38.9
Income tax expense	(4.5)	(5.6)	(12.8)	(11.7)
Net income	19.1	11.5	42.9	27.2
Net income attributable to redeemable non-controlling interests in consolidated Funds	(9.0)	(0.5)	(12.7)	(1.6)
Net income attributable to controlling interests	10.1	11.0	30.2	25.6
Quant And Solutions | Consolidated Entity Excluding Consolidated Funds
Segment Reporting Information [Line Items]
Total revenue	$ 124.9	$ 108.3	$ 243.1	$ 213.6