Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Fees receivable, net of allowance of $1,736 and $0, respectively	$ 111,784				$ 45,883				$ 111,784	$ 45,883
Reimbursable to affiliated funds	100								200
Interest Income, Related Party									100
Due from related parties	34,814				39,629				34,814	39,629
Redeemable non-controlling interests, Related Party	440,604				379,205				440,604	379,205
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	11,621	$ (5,162)	$ (21,145)	$ (9,105)	(9,406)	$ (18,478)	$ 16,705	$ 4,297	(23,791)	(6,882)	$ (15,246)
Employees
Related Party Transaction [Line Items]
Redeemable non-controlling interests, Related Party	28,200				32,900				28,200	32,900
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									(7,200)	(5,700)	(10,400)
Employee Loans
Related Party Transaction [Line Items]
Due from employees	11,100				9,200				11,100	9,200
Forgivable Loan Balances	4,800				3,300				4,800	3,300
Amortization on Forgivable Loans									$ 2,100	1,200	$ 3,200
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, net of allowance of $1,736 and $0, respectively	13,500				12,600				$ 13,500	12,600
Affiliated Entity | Fees Payable
Related Party Transaction [Line Items]
Fees payable to related parties					300					300
Investor
Related Party Transaction [Line Items]
Due to Affiliate	600				700				600	700
Other Funds
Related Party Transaction [Line Items]
Due from related parties	9,700				11,800				9,700	$ 11,800
Starboard Value LP
Related Party Transaction [Line Items]
Effective interest rate										5.00%
Interest Income, Related Party									800	$ 600
Due from related parties	$ 14,000				$ 18,700				$ 14,000	$ 18,700
Finance Period									5 years