Non-controlling Interests (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interests	$ 56	$ 1,632
Total non-controlling interest in net income	22,650	16,318
Non-redeemable non-controlling interest	1,630		$ 1,564
Redeemable non-controlling interest	996,966		601,587
CPH acquisition
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interest	920		807
Redeemable non-controlling interest	5,364		5,364
Other
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interests	98	147
Company-sponsored investment funds
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interests	(42)	1,485
Redeemable non-controlling interests	22,594	$ 14,686
Non-redeemable non-controlling interest	710		757
Redeemable non-controlling interest	$ 991,602		$ 596,223