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	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 381,369	$ 458,744
Total Derivative Assets	4,057	1,993
Total investments measured at fair value	385,426	460,737
Securities sold, not yet purchased	4,293	4,482
Contingent consideration liability	25,104	22,608
Total Derivative Liabilities	179,023	182,223
Total of Liabilities Measured at Fair Value	208,420	209,313
Fair Value, Measurements, Nonrecurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments measured at fair value	88,848	129,591
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments measured at fair value	262,788	327,645
Securities sold, not yet purchased	4,293	4,482
Total of Liabilities Measured at Fair Value	4,293	4,482
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Derivative Assets	4,057	1,993
Total investments measured at fair value	32,253	1,993
Total Derivative Liabilities	179,023	182,223
Total of Liabilities Measured at Fair Value	179,023	182,223
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments measured at fair value	1,537	1,508
Contingent consideration liability	25,104	22,608
Total of Liabilities Measured at Fair Value	25,104	22,608
Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	42,962	41,017
Equities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	41,425	39,509
Equities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,537	1,508
Alternative Investment Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	31,046	32,441
Alternative Investment Funds [Member] | Fair Value, Measurements, Nonrecurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	7,047	7,125
Alternative Investment Funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	23,999	25,316
Debt Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	61,486	74,597
Debt Funds [Member] | Fair Value, Measurements, Nonrecurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	6	6
Debt Funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	61,480	74,591
Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	135,926	188,268
Equity Funds [Member] | Fair Value, Measurements, Nonrecurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	42	39
Equity Funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	135,884	188,229
Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	109,949	122,421
Private Equity Funds [Member] | Fair Value, Measurements, Nonrecurring [Member] | NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	81,753	$ 122,421
Private Equity Funds [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 28,196