Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 240.0	$ 130.3	$ 9.1
Adjustments to reconcile net income to net cash flows from operating activities from continuing operations:
(Gain) loss from discontinued operations, excluding consolidated Funds	0.0	(0.1)	0.1
Amortization of acquired intangibles	6.6	6.6	6.6
Net earnings from Affiliates accounted for using the equity method	(16.7)	0.0	0.0
Gain on sale of investment in Affiliate	0.0	(65.7)	0.0
Deferred income taxes	25.5	(29.2)	93.3
Changes in operating assets and liabilities (excluding discontinued operations):
Net cash flows from operating activities of continuing operations	(138.5)	195.0	139.7
Net cash flows from operating activities of discontinued operations	0.0	0.1	0.0
Total net cash flows from operating activities	(138.5)	195.1	139.7
Cash flows from investing activities:
Purchase of investment securities	(186.9)	(250.3)	(145.6)
Distributions received from equity method investees	149.1	191.2	59.8
Net cash flows from investing activities of continuing operations	9.0	17.4	54.8
Net cash flows from investing activities of discontinued operations	0.0	0.0	0.0
Total net cash flows from investing activities	9.0	17.4	54.8
Cash flows from financing activities:
Payment of debt issuance costs	(1.8)	0.0	0.0
Net cash flows from financing activities of continuing operations	(95.0)	(67.4)	(96.4)
Net cash flows from financing activities of discontinued operations	0.0	0.0	0.0
Total net cash flows from financing activities	(95.0)	(67.4)	(96.4)
Net increase (decrease) in cash and cash equivalents	(224.5)	145.1	98.1
Cash and cash equivalents at beginning of period	345.5	200.4	102.3
Cash and cash equivalents at end of period (including cash at consolidated Funds classified as restricted)	121.0	345.5	200.4
Supplemental disclosure of cash flow information:
Income taxes paid	44.6	45.6	71.2
Supplemental disclosure of non-cash investing and financing transactions:
Consolidation (de-consolidation) of Funds	0.0	(105.5)	50.8
Consolidated Entity Excluding Consolidated Funds
Adjustments to reconcile net income to net cash flows from operating activities from continuing operations:
(Gain) loss from discontinued operations, excluding consolidated Funds	0.0	(0.1)	0.1
Amortization of acquired intangibles	6.6	6.6	6.6
Depreciation and amortization	17.2	14.5	11.7
Amortization of debt-related costs	3.7	3.3	3.1
Amortization and revaluation of non-cash compensation awards	(13.4)	198.8	192.3
Net earnings from Affiliates accounted for using the equity method	(2.8)	(2.7)	(14.5)
Distributions received from equity method Affiliates	2.7	11.9	15.4
Revaluation of DTA Deed	0.0	(20.0)	(51.8)
Impact of Tax Act on deferred income taxes	0.0	0.0	121.1
Deferred income taxes	25.8	(24.8)	(30.1)
(Gains) losses on other investments	(38.0)	6.1	(37.4)
Changes in operating assets and liabilities (excluding discontinued operations):
(Increase) decrease in investment advisory fees receivable and other amounts due from OM plc	7.1	49.5	(44.7)
(Increase) decrease in other receivables, prepayments, deposits and other assets	(24.4)	21.9	(31.6)
Increase (decrease) in accrued incentive compensation and other liabilities and amounts due to OM plc	(264.9)	(37.3)	65.2
Increase (decrease) in accounts payable, accrued expenses and accrued income taxes	(50.1)	(46.1)	15.3
Net cash flows from operating activities of continuing operations	(106.6)	252.3	224.9
Cash flows from investing activities:
Purchase of fixed assets, excluding discontinued operations	(33.9)	(21.7)	(13.7)
Proceeds from sale of investment in Affiliate	5.0	105.0	0.0
Business acquisitions, net of cash acquired	0.0	0.0	(1.9)
Purchase of investment securities	(26.5)	(103.9)	(84.6)
Sale of investment securities	73.1	78.2	89.4
Cash flows from financing activities:
Proceeds from third party and non-recourse borrowings	505.0	15.0	76.0
Repayment of third party and non-recourse borrowings	(330.0)	(48.5)	(42.5)
Payment to OM plc for promissory notes	0.0	4.5	0.0
Payment to OM plc for deferred tax arrangement	(32.7)	0.0	(45.6)
Payment to OM plc for co-investment redemptions	(5.1)	(3.9)	(4.8)
Repurchase of common stock	(239.8)	(71.2)	(74.1)
Dividends paid to shareholders	(24.5)	(31.8)	(27.5)
Dividends paid to related parties	(11.5)	(10.7)	(11.3)
Supplemental disclosure of cash flow information:
Interest Paid, Excluding Capitalized Interest, Operating Activities	28.4	22.2	22.1
Consolidated Funds
Cash flows from operating activities:
Net income (loss) attributable to non-controlling interests in consolidated Funds	(16.1)	6.1	(4.9)
Adjustments to reconcile net income to net cash flows from operating activities from continuing operations:
(Gains) losses on other investments	6.9	9.0	(5.6)
Changes in operating assets and liabilities (excluding discontinued operations):
(Increase) decrease in receivables and other assets	7.5	(14.1)	(0.8)
Increase (decrease) in accounts payable and other liabilities	(7.9)	13.0	2.1
Net cash flows from operating activities of continuing operations	(31.9)	(57.3)	(85.2)
Cash flows from investing activities:
Purchase of investment securities	(12.6)	0.0	0.0
Distributions received from equity method investees	3.9	0.0	0.0
Consolidation (de-consolidation) of Funds	0.0	(40.2)	65.6
Cash flows from financing activities:
Redeemable non-controlling interest capital raised	37.9	88.6	33.4
Supplemental disclosure of non-cash investing and financing transactions:
Payable for securities purchased by a consolidated Fund	4.0	10.8	0.0
Consolidated Funds
Cash flows from financing activities:
Non-controlling interest capital raised	12.6	0.0	0.0
Non-controlling interest capital redeemed	3.4	0.0	0.0
Redeemable non-controlling interest capital redeemed	$ (1.7)	$ (0.4)	$ 0.0