Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Consolidated Funds	Common Stock Investments in unconsolidated Funds	Additional paid-in capital Investments in unconsolidated Funds	Retained earnings (deficit) Investments in unconsolidated Funds	Accumulated other comprehensive income (loss) Investments in unconsolidated Funds	Total stockholders’ equity Investments in unconsolidated Funds	Non- controlling interests Investments in unconsolidated Funds	Non- controlling interests Consolidated Funds
Beginning balance (in shares) at Dec. 31, 2018			105.2
Beginning balance at Dec. 31, 2018	$ 134.2		$ 0.1	$ 764.6	$ (640.5)	$ (20.9)	$ 103.3	$ 1.6	$ 29.3
Increase (Decrease) in Stockholders' Equity
Issuance of common stock (in shares)			0.2
Repurchase of common stock (in shares)			(13.8)
Repurchase of common stock	(183.8)			(183.8)			(183.8)
Capital contributions (redemptions)	4.0	$ 37.3							4.0
Equity-based compensation	4.4			4.4			4.4
Foreign currency translation adjustment	(0.1)					(0.1)	(0.1)
Amortization related to derivative securities, net of tax	1.2					1.2	1.2
Other changes in non-controlling interests	0.2							0.2
Dividends	(18.4)				(18.4)		(18.4)
Net income attributable to controlling interests	80.7
Net income (loss)	80.1				80.7		80.7		(0.6)
Ending balance (in shares) at Jun. 30, 2019			91.6
Ending balance at Jun. 30, 2019	21.8		$ 0.1	585.2	(578.2)	(19.8)	(12.7)	1.8	32.7
Beginning balance at Dec. 31, 2018		41.9
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	4.0	37.3							4.0
Dividends	(18.4)				(18.4)		(18.4)
Net income (loss)		2.6
Ending balance at Jun. 30, 2019		81.8
Beginning balance at Dec. 31, 2018	176.1
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Issuance of common stock	0.0
Repurchase of common stock	(183.8)
Capital contributions (redemptions)	41.3
Equity-based compensation	4.4
Foreign currency translation adjustment	(0.1)
Amortization related to derivative securities, net of tax	1.2
Dividends	(18.4)
Net income (loss)	82.7
Ending balance at Jun. 30, 2019	103.6
Beginning balance (in shares) at Mar. 31, 2019			91.9
Beginning balance at Mar. 31, 2019	8.4		$ 0.1	587.3	(597.0)	(19.8)	(29.4)	1.8	36.0
Increase (Decrease) in Stockholders' Equity
Repurchase of common stock (in shares)			(0.3)
Repurchase of common stock	(3.3)			(3.3)			(3.3)
Capital contributions (redemptions)	4.0	37.7							4.0
Equity-based compensation	1.2			1.2			1.2
Foreign currency translation adjustment	(0.6)					(0.6)	(0.6)
Amortization related to derivative securities, net of tax	0.6					0.6	0.6
Dividends	(9.2)				(9.2)		(9.2)
Net income attributable to controlling interests	28.0
Net income (loss)	20.7				28.0		28.0		(7.3)
Ending balance (in shares) at Jun. 30, 2019			91.6
Ending balance at Jun. 30, 2019	21.8		$ 0.1	585.2	(578.2)	(19.8)	(12.7)	1.8	32.7
Beginning balance at Mar. 31, 2019		43.2
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	4.0	37.7							4.0
Dividends	(9.2)				(9.2)		(9.2)
Net income (loss)		0.9
Ending balance at Jun. 30, 2019		81.8
Beginning balance at Mar. 31, 2019	51.6
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Repurchase of common stock	(3.3)
Capital contributions (redemptions)	41.7
Equity-based compensation	1.2
Foreign currency translation adjustment	(0.6)
Amortization related to derivative securities, net of tax	0.6
Net de-consolidation of Funds	0.0
Dividends	(9.2)
Net income (loss)	21.6
Ending balance at Jun. 30, 2019	103.6
Beginning balance (in shares) at Dec. 31, 2019			85.9
Beginning balance at Dec. 31, 2019	114.5		$ 0.1	534.3	(452.5)	(17.5)	64.4	1.3	48.8
Increase (Decrease) in Stockholders' Equity
Issuance of common stock (in shares)			0.1
Retirement of common stock (in shares)			(0.2)
Repurchase of common stock (in shares)			(5.7)
Repurchase of common stock	(35.3)			(35.3)			(35.3)
Capital contributions (redemptions)	1.1	0.4							1.1
Equity-based compensation	1.6			1.6			1.6
Foreign currency translation adjustment	(1.8)					(1.8)	(1.8)
Amortization related to derivative securities, net of tax	1.1					1.1	1.1
Other changes in non-controlling interests	0.1							0.1
Dividends	(9.1)				(9.1)		(9.1)
Net income attributable to controlling interests	51.5
Net income (loss)	80.4						51.5		28.9
Ending balance (in shares) at Jun. 30, 2020			80.1
Ending balance at Jun. 30, 2020	152.6		$ 0.1	500.6	(410.1)	(18.2)	72.4	1.4	78.8
Beginning balance at Dec. 31, 2019		83.9
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	1.1	0.4							1.1
Dividends	(9.1)				(9.1)		(9.1)
Net income (loss)		(4.4)
Ending balance at Jun. 30, 2020		79.9
Beginning balance at Dec. 31, 2019	198.4
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Issuance of common stock	0.0
Repurchase of common stock	(35.3)
Capital contributions (redemptions)	1.5
Equity-based compensation	1.6
Foreign currency translation adjustment	(1.8)
Amortization related to derivative securities, net of tax	1.1
Dividends	(9.1)
Net income (loss)	76.0
Ending balance at Jun. 30, 2020	232.5
Beginning balance (in shares) at Mar. 31, 2020			82.5
Beginning balance at Mar. 31, 2020	119.3		$ 0.1	516.2	(428.3)	(19.1)	68.9	1.3	49.1
Increase (Decrease) in Stockholders' Equity
Issuance of common stock (in shares)			0.1
Repurchase of common stock (in shares)			(2.5)
Repurchase of common stock	(16.1)			(16.1)			(16.1)
Capital contributions (redemptions)	0.9	(0.8)							0.9
Equity-based compensation	0.5			0.5			0.5
Foreign currency translation adjustment	0.3					0.3	0.3
Amortization related to derivative securities, net of tax	0.6					0.6	0.6
Other changes in non-controlling interests	0.1							0.1
Dividends	(0.7)				(0.7)		(0.7)
Net income attributable to controlling interests	18.9
Net income (loss)	47.7				18.9		18.9		28.8
Ending balance (in shares) at Jun. 30, 2020			80.1
Ending balance at Jun. 30, 2020	152.6		$ 0.1	$ 500.6	(410.1)	$ (18.2)	72.4	$ 1.4	78.8
Beginning balance at Mar. 31, 2020		74.5
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	0.9	(0.8)							$ 0.9
Dividends	(0.7)				$ (0.7)		$ (0.7)
Net income (loss)		6.2
Ending balance at Jun. 30, 2020		$ 79.9
Beginning balance at Mar. 31, 2020	193.8
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Issuance of common stock	0.0
Repurchase of common stock	(16.1)
Capital contributions (redemptions)	0.1
Equity-based compensation	0.5
Foreign currency translation adjustment	0.3
Amortization related to derivative securities, net of tax	0.6
Dividends	(0.7)
Net income (loss)	53.9
Ending balance at Jun. 30, 2020	$ 232.5