Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Fees receivable	$ 111,756		$ 111,756		$ 111,784
Due from related parties	32,509		32,509		34,814
Redeemable non-controlling interests, Related Party	203,212		203,212		440,604
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(5,290)	$ (5,162)	(41,053)	$ (35,412)
Employees
Related Party Transaction [Line Items]
Redeemable non-controlling interests, Related Party	27,700		27,700		28,200
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(4,500)	(1,600)	(8,900)	(7,200)
Employee Loans
Related Party Transaction [Line Items]
Due from employees	14,800		14,800		11,100
Forgivable Loan Balances	7,100		7,100		4,800
Amortization on Forgivable Loans	800	600	$ 2,200	$ 1,600
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	19,400		$ 19,400		13,500
Investor
Related Party Transaction [Line Items]
Due to Affiliate	600		600		600
Other Funds
Related Party Transaction [Line Items]
Due from related parties	9,700		9,700		9,700
Starboard Value LP
Related Party Transaction [Line Items]
Effective interest rate				5.00%
Interest Income, Related Party	100	$ 200	300	$ 600
Due from related parties	$ 7,800		$ 7,800		$ 14,000
Finance Period			5 years