Non-controlling Interests (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interests	$ 58	$ 62	$ 74	$ 118
Total non-controlling interest in net income	7,757	261	17,873	22,911
Non-redeemable non-controlling interest	1,020		1,020		$ 949
Redeemable non-controlling interest	215,634		215,634		148,809
CPH acquisition
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interest	1,020		1,020		949
Redeemable non-controlling interest	2,888		2,888		2,888
Other
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interests	58	73	74	171
Company-sponsored investment funds
Noncontrolling Interest [Line Items]
Non-redeemable non-controlling interests	0	(11)	0	(53)
Redeemable non-controlling interests	7,699	$ 199	17,799	$ 22,793
Non-redeemable non-controlling interest	0		0		0
Redeemable non-controlling interest	$ 212,746		$ 212,746		$ 145,921