Non-controlling Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Non-redeemable non-controlling interests	$ 9,632	$ 11,398	$ 6,375
Net income of consolidated entities attributable to non-controlling interests	58,397	21,488	6,375
Non-redeemable non-controlling interest	1,564	36,172
Redeemable non-controlling interest	601,587	392,959
CPH Acquisition [Member]
Variable Interest Entity [Line Items]
Redeemable non-controlling interest	5,364	8,665
Consolidated Private Equity Fund [Member]
Variable Interest Entity [Line Items]
Non-redeemable non-controlling interests	0	0	5,940
Other Investments [Member]
Variable Interest Entity [Line Items]
Non-redeemable non-controlling interests	279	312	435
Non-redeemable non-controlling interest	807	1,550
Company-Sponsored Investment Funds [Member]
Variable Interest Entity [Line Items]
Non-redeemable non-controlling interests	9,353	11,086	0
Redeemable non-controlling interests	48,765	10,090	$ 0
Non-redeemable non-controlling interest	757	34,622
Redeemable non-controlling interest	$ 596,223	$ 384,294