Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Fees receivable	$ 138,462		$ 138,462		$ 111,784
Due from related parties	32,826		32,826		34,814
Redeemable non-controlling interests, Related Party	412,067		412,067		440,604
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(24,607)	$ (21,145)	(35,763)	$ (30,250)
Employees
Related Party Transaction [Line Items]
Redeemable non-controlling interests, Related Party	22,400		22,400		28,200
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(1,500)	(3,600)	(4,300)	(5,500)
Employee Loans
Related Party Transaction [Line Items]
Due from employees	14,700		14,700		11,100
Forgivable Loan Balances	7,400		7,400		4,800
Amortization on Forgivable Loans	800	600	$ 1,400	$ 1,000
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	16,500		$ 16,500		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	10,200		10,200		9,700
Starboard Value LP
Related Party Transaction [Line Items]
Effective interest rate				5.00%
Interest Income, Related Party	100	$ 200	200	$ 400
Due from related parties	$ 7,800		$ 7,800		$ 14,000
Finance Period			5 years