Fair Value Measurements - Schedule of Classification of Investments and Certain Other Assets and Liabilities Measured at Fair Value on Recurring Basis and Investments Measured at NAV (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	$ 420,964	$ 458,744
Total Derivative Assets	2,595	1,993
Total investments measured at fair value	423,559	460,737
Securities sold, not yet purchased	4,527	4,482
Contingent consideration liability	25,539	22,608
Total Derivative Liabilities	176,300	182,223
Total of Liabilities Measured at Fair Value	206,366	209,313
Fair Value, Measurements, Recurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total investments measured at fair value	86,898	129,591
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total investments measured at fair value	330,994	327,645
Securities sold, not yet purchased	4,527	4,482
Total of Liabilities Measured at Fair Value	4,527	4,482
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Derivative Assets	2,595	1,993
Total investments measured at fair value	2,595	1,993
Total Derivative Liabilities	176,300	182,223
Total of Liabilities Measured at Fair Value	176,300	182,223
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total investments measured at fair value	3,072	1,508
Contingent consideration liability	25,539	22,608
Total of Liabilities Measured at Fair Value	25,539	22,608
Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7
Debt [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7
Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	46,137	41,017
Equities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	43,065	39,509
Equities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	3,072	1,508
Alternative Investment Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	23,456	32,441
Alternative Investment Funds [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7,808	7,125
Alternative Investment Funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	15,648	25,316
Debt Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	86,294	74,597
Debt Funds [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	7	6
Debt Funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	86,287	74,591
Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	186,034	188,268
Equity Funds [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	47	39
Equity Funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	185,987	188,229
Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	79,036	122,421
Private Equity Funds [Member] | Fair Value, Measurements, Recurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	$ 79,036	$ 122,421