Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Fees receivable	$ (101,508)		$ (101,508)		$ (111,946)
Due to Other Related Parties	500		500
Interest Income, Related Party	100		0
Due from related parties	27,849		27,849		33,870
Redeemable non-controlling interests, Related Party	348,424		348,424		216,923
Net income (loss) attributable to non-controlling interests in consolidated subsidiaries and investment funds	6,848		4,187	$ (22,501)
Employees
Related Party Transaction [Line Items]
Redeemable non-controlling interests, Related Party	34,900		34,900		25,100
Net income (loss) attributable to non-controlling interests in consolidated subsidiaries and investment funds	(3,600)	$ (4,100)	(4,700)	(8,400)
Employee Loans
Related Party Transaction [Line Items]
Due from employees	14,200		14,200		17,000
Forgivable Loan Balances	7,400		7,400		8,800
Amortization on Forgivable Loans	1,000	800	$ 2,800	$ 2,200
Employee Loans | Minimum
Related Party Transaction [Line Items]
Forgivable Loans, Vesting Period			1 year
Employee Loans | Maximum
Related Party Transaction [Line Items]
Forgivable Loans, Vesting Period			3 years
Affiliated Entity
Related Party Transaction [Line Items]
Fees receivable	(19,900)		$ (19,900)		(19,400)
Investor
Related Party Transaction [Line Items]
Due to Affiliate	300		300		600
Other Funds
Related Party Transaction [Line Items]
Due from related parties	6,600		6,600		8,900
Starboard Value LP
Related Party Transaction [Line Items]
Effective interest rate				5.00%
Interest Income, Related Party	100	$ 100	300	$ 300
Due from related parties	$ 7,000		$ 7,000		$ 7,700
Finance Period			5 years