Segment Information - Schedule of Operating Results by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment information
Total revenue	$ 505.6	$ 426.6	$ 417.2
Operating income	135.5	106.0	167.9
Income before taxes	125.7	96.5	144.8
Income tax expense	(38.9)	(29.4)	(44.2)
Net income	86.8	67.1	100.6
Net income attributable to non-controlling interests in consolidated Funds	(1.8)	(1.3)	0.0
Net income attributable to controlling interests	85.0	65.8	100.6
Hold Co
Segment information
Fixed compensation and benefits	10.0	9.2	11.4
Depreciation and amortization			0.4
General and administrative expense	9.4	9.9	10.4
Consolidated Funds
Segment information
Total revenue	3.1	3.0	0.4
Net consolidated Funds’ investment gains (losses)	3.9	4.1	(0.4)
Consolidated Entity Excluding Consolidated Funds
Segment information
Fixed compensation and benefits	265.5	217.9	159.2
Depreciation and amortization	18.5	17.3	18.5
Investment income (loss)	2.2	(0.1)	0.2
Interest income	3.5	6.1	0.8
Interest expense	19.4	19.6	20.5
Loss on extinguishment of debt	0.0	0.0	(3.2)
Net income	86.8	67.1	100.6
Quant & Solutions
Segment information
Total revenue	505.6	426.6	417.2
Fixed compensation and benefits	90.7	86.6	79.0
Variable compensation	119.9	102.2	96.0
Acadian LLC key employee distributions	9.7	5.1	5.1
Depreciation and amortization	18.1	17.3	18.1
Other segment items	87.9	80.3	68.4
Operating income	176.2	132.1	150.2
Unallocated corporate expenses	(19.4)	(19.1)	(22.2)
Adjustments and reconciling items	1.9	(7.1)	(0.1)
Non-cash compensation expenses for Acadian LLC key employee equity and profit interest revaluations	(23.2)	0.1	40.0
Investment income (loss)	2.2	(0.1)	0.2
Interest income	3.5	6.1	0.8
Interest expense	(19.4)	(19.6)	(20.5)
Loss on extinguishment of debt	0.0	0.0	(3.2)
Income before taxes	125.7	96.5	144.8
Income tax expense	(38.9)	(29.4)	(44.2)
Net income	86.8	67.1	100.6
Net income attributable to non-controlling interests in consolidated Funds	(1.8)	(1.3)	0.0
Net income attributable to controlling interests	85.0	65.8	100.6
Quant & Solutions | Consolidated Funds
Segment information
Total revenue	3.1	3.0	0.4
Net consolidated Funds’ investment gains (losses)	3.9	4.1	(0.4)
Quant & Solutions | Consolidated Entity Excluding Consolidated Funds
Segment information
Total revenue	$ 502.5	$ 423.6	$ 416.8