Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Cash flows from operating activities:
Consolidated net income	$ 69.9	$ 46.2
Adjustments to reconcile net income (loss) attributable to redeemable non-controlling interests of consolidated Funds to net cash flows from operating activities of consolidated Funds:
Total net cash flows from operating activities	(11.1)	74.9
Cash Flows From Investing Activities Of Consolidated Funds [Abstract]
Net deconsolidation of Funds	(142.9)	0.0
Net cash flows from investing activities	(41.1)	(48.3)
Cash flows from financing activities of consolidated Funds:
Total net cash flows from financing activities	92.0	(103.0)
Effect of foreign exchange rate changes on cash and cash equivalents	0.4	0.1
Net increase (decrease) in cash and cash equivalents	40.2	(76.3)
Cash and cash equivalents at beginning of period	98.5	147.6
Cash and cash equivalents at end of period	138.7	71.3
Cash and cash equivalents
Cash and cash equivalents at end of period	138.7	71.3
Supplemental disclosure of cash flow information:
Income taxes paid	28.8	33.0
Supplemental disclosure of non-cash investing and financing transactions:
Excise tax on repurchase of common stock	0.5	0.8
Consolidated Entity Excluding Consolidated Funds
Cash flows from operating activities:
Consolidated net income	69.9	46.2
Less: Net income attributable to redeemable non-controlling interests in consolidated Funds	(24.6)	(3.7)
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	12.5	14.1
Amortization of debt-related costs	3.5	3.3
Amortization and revaluation of non-cash compensation awards	40.1	25.1
Deferred income taxes	3.1	(8.7)
(Gains) on other investments	(10.7)	(12.4)
Changes in operating assets and liabilities:
Decrease in investment advisory fees receivable	25.7	24.2
(Increase) in other receivables, prepayments, deposits and other assets	(12.3)	(2.0)
(Decrease) in accrued incentive compensation, operating lease liabilities and other liabilities	(39.1)	(21.9)
(Decrease) in accounts payable, accrued expenses and accrued income taxes	(4.6)	(5.1)
Adjustments to reconcile net income (loss) attributable to redeemable non-controlling interests of consolidated Funds to net cash flows from operating activities of consolidated Funds:
Total net cash flows from operating activities	63.5	59.1
Cash flows from investing activities:
Additions of fixed assets	(8.2)	(7.4)
Purchase of investment securities	(17.8)	(47.5)
Sale of investment securities	34.7	6.6
Cash flows from financing activities:
Proceeds from revolving credit facility	137.0	139.0
Repayment of revolving credit facility	(137.0)	(139.0)
Payment for debt issuance costs	0.0	(0.6)
Payment to OM plc for co-investment redemptions	0.0	(0.2)
Repurchase of common stock	(48.8)	(94.9)
Withholding tax payments related to stock option exercise and restricted stock vesting	(0.2)	(7.2)
Cash and cash equivalents
Cash and cash equivalents	117.3	53.6
Supplemental disclosure of cash flow information:
Interest paid (excluding consolidated Funds)	14.5	15.0
Consolidated Entity Excluding Consolidated Funds | Nonrelated Party
Cash flows from financing activities:
Dividends paid to stockholders	(0.7)	(0.7)
Consolidated Entity Excluding Consolidated Funds | Related Party
Cash flows from financing activities:
Dividends paid to stockholders	(0.4)	(0.5)
Consolidated Funds
Cash flows from operating activities:
Less: Net income attributable to redeemable non-controlling interests in consolidated Funds	24.6	3.7
Adjustments to reconcile net income to net cash flows from operating activities:
(Gains) on other investments	(19.9)	(2.0)
Adjustments to reconcile net income (loss) attributable to redeemable non-controlling interests of consolidated Funds to net cash flows from operating activities of consolidated Funds:
Purchase of investments	(593.1)	(46.0)
Sale of investments	398.5	60.3
(Increase) decrease in receivables and other assets	3.2	(1.8)
Increase in accounts payable and other liabilities	112.1	1.6
Total net cash flows from operating activities	(74.6)	15.8
Cash Flows From Investing Activities Of Consolidated Funds [Abstract]
Net deconsolidation of Funds	49.8	0.0
Cash flows from financing activities of consolidated Funds:
Redeemable non-controlling interest capital raised	145.8	1.1
Redeemable non-controlling interest capital redeemed	(3.7)	0.0
Cash and cash equivalents
Cash and cash equivalents	$ 21.4	$ 17.7