Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Consolidated Funds	Ordinary shares Investments in unconsolidated Funds	Shareholders’ equity Investments in unconsolidated Funds	Accumulated other comprehensive income (loss) Investments in unconsolidated Funds	Total shareholders’ equity Investments in unconsolidated Funds	Non- controlling interests Investments in unconsolidated Funds	Non- controlling interests Consolidated Funds
Beginning balance (in shares) at Dec. 31, 2017			109.7
Beginning balance at Dec. 31, 2017	$ 127.3		$ 0.1	$ 96.9	$ (21.6)	$ 75.4	$ 1.3	$ 50.6
Increase (Decrease) in Stockholders' Equity
Issuance of ordinary shares (in shares)			1.0
Repurchase of ordinary shares (in shares)			(1.8)
Repurchase of ordinary shares	(27.4)			(27.4)		(27.4)
Capital contributions (redemptions)	9.2			(0.1)		(0.1)		9.3
Equity-based compensation	2.9			2.9		2.9
Foreign currency translation adjustment	(0.8)				(0.8)	(0.8)
Amortization related to derivative securities, net of tax	1.2				1.2	1.2
Business acquisition	0.1						0.1
Dividends	(21.0)			(21.0)		(21.0)
Net income	57.6			59.4		59.4		(1.8)
Ending balance (in shares) at Jun. 30, 2018			108.9
Ending balance at Jun. 30, 2018	149.1		$ 0.1	110.7	(21.2)	89.6	1.4	58.1
Beginning balance at Dec. 31, 2017		$ 44.0
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)		3.8
Net de-consolidation of Funds		41.5
Net income		(0.3)
Ending balance at Jun. 30, 2018		6.0
Beginning balance at Dec. 31, 2017	171.3
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Issuance of ordinary shares	0.0
Repurchase of ordinary shares	(27.4)
Capital contributions (redemptions)	13.0
Equity-based compensation	2.9
Foreign currency translation adjustment	(0.8)
Amortization related to derivative securities, net of tax	1.2
Net de-consolidation of Funds	41.5
Dividends	(21.0)
Net income (loss)	57.3
Ending balance at Jun. 30, 2018	155.1
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Net income attributable to controlling interests	59.4
Beginning balance (in shares) at Mar. 31, 2018			110.5
Beginning balance at Mar. 31, 2018	172.0		$ 0.1	142.8	(20.2)	122.7	1.4	47.9
Increase (Decrease) in Stockholders' Equity
Repurchase of ordinary shares (in shares)			(1.6)
Repurchase of ordinary shares	(24.8)			(24.8)		(24.8)
Capital contributions (redemptions)	9.3							9.3
Equity-based compensation	1.6			1.6		1.6
Foreign currency translation adjustment	(1.6)				(1.6)	(1.6)
Amortization related to derivative securities, net of tax	0.6				0.6	0.6
Dividends	(11.0)			(11.0)		(11.0)
Net income	3.0			2.1		2.1		0.9
Ending balance (in shares) at Jun. 30, 2018			108.9
Ending balance at Jun. 30, 2018	149.1		$ 0.1	110.7	(21.2)	89.6	1.4	58.1
Beginning balance at Mar. 31, 2018		37.2
Increase (Decrease) in redeemable non-controlling interest in consolidated Funds
Capital contributions (redemptions)		3.7
Net de-consolidation of Funds		(34.4)
Net income		(0.5)
Ending balance at Jun. 30, 2018		6.0
Beginning balance at Mar. 31, 2018	209.2
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Repurchase of ordinary shares	(24.8)
Capital contributions (redemptions)	13.0
Equity-based compensation	1.6
Foreign currency translation adjustment	(1.6)
Amortization related to derivative securities, net of tax	0.6
Net de-consolidation of Funds	(34.4)
Dividends	(11.0)
Net income (loss)	2.5
Ending balance at Jun. 30, 2018	155.1
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Net income attributable to controlling interests	2.1
Beginning balance (in shares) at Dec. 31, 2018			105.2
Beginning balance at Dec. 31, 2018	134.2		$ 0.1	124.1	(20.9)	103.3	1.6	29.3
Increase (Decrease) in Stockholders' Equity
Issuance of ordinary shares (in shares)			0.2
Repurchase of ordinary shares (in shares)			(13.8)
Repurchase of ordinary shares	(183.8)			(183.8)		(183.8)
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
Business acquisition	0.2						0.2
Dividends	(18.4)			(18.4)		(18.4)
Net income	80.1					80.7		(0.6)
Ending balance (in shares) at Jun. 30, 2019			91.6
Ending balance at Jun. 30, 2019	21.8		$ 0.1	7.0	(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
Net income		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 ordinary shares	0.0
Repurchase of ordinary shares	(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
Net de-consolidation of Funds	0.0
Dividends	(18.4)
Net income (loss)	82.7
Ending balance at Jun. 30, 2019	103.6
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Net income attributable to controlling interests	80.7
Beginning balance (in shares) at Mar. 31, 2019			91.9
Beginning balance at Mar. 31, 2019	8.4		$ 0.1	(9.7)	(19.8)	(29.4)	1.8	36.0
Increase (Decrease) in Stockholders' Equity
Repurchase of ordinary shares (in shares)			(0.3)
Repurchase of ordinary shares	(3.3)			(3.3)		(3.3)
Capital contributions (redemptions)	4.0							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	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	$ 7.0	$ (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)		37.7
Net income		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 ordinary shares	(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
Dividends	(9.2)
Net income (loss)	21.6
Ending balance at Jun. 30, 2019	103.6
Increase (Decrease) in total equity and redeemable non-controlling interest in consolidated Funds
Net income attributable to controlling interests	$ 28.0