Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Consolidated Funds	Common Stock Consolidated Entity Excluding Consolidated Funds	Additional paid-in capital	Additional paid-in capital Consolidated Entity Excluding Consolidated Funds	Retained earnings (deficit) Consolidated Entity Excluding Consolidated Funds	Accumulated other comprehensive income (loss) Consolidated Entity Excluding Consolidated Funds	Total stockholders’ equity	Total stockholders’ equity Consolidated Entity Excluding Consolidated Funds	Non- controlling interests Consolidated Entity Excluding Consolidated 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)			(16.6)
Repurchase of common stock	(209.3)				(209.3)				(209.3)
Capital contributions (redemptions)	4.9	$ 36.3									4.9
Equity-based compensation	5.1				5.1				5.1
Foreign currency translation adjustment	(0.9)						(0.9)		(0.9)
Amortization related to derivative securities, net of tax	1.8						1.8		1.8
Other changes in non-controlling interests	0.3									0.3
Dividends	(27.3)					(27.3)			(27.3)
Net income attributable to controlling interests	156.1
Net income (loss)	162.0					156.1			156.1		5.9
Ending balance (in shares) at Sep. 30, 2019			88.8
Ending balance at Sep. 30, 2019	70.8		$ 0.1		560.4	(511.7)	(20.0)		28.8	1.9	40.1
Beginning balance at Dec. 31, 2018		41.9
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	4.9	36.3									4.9
Net income (loss)		3.7
Ending balance at Sep. 30, 2019		81.9
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	(209.3)
Capital contributions (redemptions)	41.2
Equity-based compensation	5.1
Foreign currency translation adjustment	(0.9)
Amortization related to derivative securities, net of tax	1.8
Other changes in non-controlling interests	0.3									0.3
Dividends	(27.3)
Net income (loss)	165.7
Ending balance at Sep. 30, 2019	152.7
Beginning balance (in shares) at Jun. 30, 2019			91.6
Beginning balance at Jun. 30, 2019	21.8		$ 0.1		585.2	(578.2)	(19.8)		(12.7)	1.8	32.7
Increase (Decrease) in Stockholders' Equity
Repurchase of common stock (in shares)			(2.8)
Repurchase of common stock	(25.5)				(25.5)				(25.5)
Capital contributions (redemptions)	0.9	(1.0)									0.9
Equity-based compensation	0.7				0.7				0.7
Foreign currency translation adjustment	(0.8)						(0.8)		(0.8)
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	(8.9)					(8.9)			(8.9)
Net income attributable to controlling interests	75.4
Net income (loss)	81.9					75.4			75.4		6.5
Ending balance (in shares) at Sep. 30, 2019			88.8
Ending balance at Sep. 30, 2019	70.8		$ 0.1		560.4	(511.7)	(20.0)		28.8	1.9	40.1
Beginning balance at Jun. 30, 2019		81.8
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	0.9	(1.0)									0.9
Net income (loss)		1.1
Ending balance at Sep. 30, 2019		81.9
Beginning balance at Jun. 30, 2019	103.6
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Repurchase of common stock	(25.5)
Capital contributions (redemptions)	(0.1)
Equity-based compensation	0.7
Foreign currency translation adjustment	(0.8)
Amortization related to derivative securities, net of tax	0.6
Other changes in non-controlling interests	0.1									0.1
Dividends	(8.9)
Net income (loss)	83.0
Ending balance at Sep. 30, 2019	152.7
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
Issuance of common stock	0.2			$ 0.2				$ 0.2
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)	1.4	130.1									1.4
Equity-based compensation	2.0				2.0				2.0
Foreign currency translation adjustment	(0.4)						(0.4)		(0.4)
Amortization related to derivative securities, net of tax	1.7						1.7		1.7
Other changes in non-controlling interests	0.1									0.1
Dividends	(9.9)					(9.9)			(9.9)
Net income attributable to controlling interests	88.7
Net income (loss)	111.5					88.7			88.7		22.8
Ending balance (in shares) at Sep. 30, 2020			80.1
Ending balance at Sep. 30, 2020	185.8		$ 0.1		501.2	(373.7)	(16.2)		111.4	1.4	73.0
Beginning balance at Dec. 31, 2019		83.9
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	1.4	130.1									1.4
Net de-consolidation of Funds		(126.8)
Net income (loss)		(1.6)
Ending balance at Sep. 30, 2020		85.6
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	0.2
Repurchase of common stock	(35.3)
Capital contributions (redemptions)	131.5
Equity-based compensation	2.0
Foreign currency translation adjustment	(0.4)
Amortization related to derivative securities, net of tax	1.7
Other changes in non-controlling interests	0.1									0.1
Net de-consolidation of Funds	(126.8)
Dividends	(9.9)
Net income (loss)	109.9
Ending balance at Sep. 30, 2020	271.4
Beginning balance (in shares) at Jun. 30, 2020			80.1
Beginning balance at Jun. 30, 2020	152.6		$ 0.1		500.6	(410.1)	(18.2)		72.4	1.4	78.8
Increase (Decrease) in Stockholders' Equity
Issuance of common stock	0.2			$ 0.2				$ 0.2
Capital contributions (redemptions)	0.3	129.7									0.3
Equity-based compensation	0.4				0.4				0.4
Foreign currency translation adjustment	1.4						1.4		1.4
Amortization related to derivative securities, net of tax	0.6						0.6		0.6
Other changes in non-controlling interests	0.0									0.0
Dividends	(0.8)					(0.8)			(0.8)
Net income attributable to controlling interests	37.2
Net income (loss)	31.1					37.2			37.2		(6.1)
Ending balance (in shares) at Sep. 30, 2020			80.1
Ending balance at Sep. 30, 2020	185.8		$ 0.1		$ 501.2	$ (373.7)	$ (16.2)		$ 111.4	1.4	73.0
Beginning balance at Jun. 30, 2020		79.9
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)	0.3	129.7									$ 0.3
Net de-consolidation of Funds		(126.8)
Net income (loss)		2.8
Ending balance at Sep. 30, 2020		$ 85.6
Beginning balance at Jun. 30, 2020	232.5
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Issuance of common stock	0.2
Repurchase of common stock	0.0
Capital contributions (redemptions)	130.0
Equity-based compensation	0.4
Foreign currency translation adjustment	1.4
Amortization related to derivative securities, net of tax	0.6
Other changes in non-controlling interests	0.0									$ 0.0
Net de-consolidation of Funds	(126.8)
Dividends	(0.8)
Net income (loss)	33.9
Ending balance at Sep. 30, 2020	$ 271.4