Consolidated Sponsored Investment Products - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets
Total assets measured at fair value	$ 101,578	$ 257,368
Level 1 [Member]
Assets
Total assets measured at fair value	101,578	257,368
Level 2 [Member]
Assets
Total assets measured at fair value	0	0
Level 3 [Member]
Assets
Total assets measured at fair value	0	0
Consolidated Sponsored Investment Products [Member]
Assets
Derivatives	4,236
Liabilities
Derivatives	1,634
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member]
Assets
Derivatives	771	381
Total assets measured at fair value	324,106	237,033
Liabilities
Derivatives	972	191
Short sales	5,409	8,165
Total liabilities measured at fair value	6,381	8,356
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Debt Securities [Member]
Assets
Investments	152,553	136,115
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Equity securities [Member]
Assets
Investments	170,782	100,537
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets
Derivatives	33	154
Total assets measured at fair value	163,019	82,571
Liabilities
Derivatives	128	191
Short sales	5,334	7,491
Total liabilities measured at fair value	5,462	7,682
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Debt Securities [Member]
Assets
Investments	0	0
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Equity securities [Member]
Assets
Investments	162,986	82,417
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets
Derivatives	738	227
Total assets measured at fair value	159,690	153,397
Liabilities
Derivatives	844	0
Short sales	75	674
Total liabilities measured at fair value	919	674
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Debt Securities [Member]
Assets
Investments	151,156	135,050
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Equity securities [Member]
Assets
Investments	7,796	18,120
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets
Derivatives	0	0
Total assets measured at fair value	1,397	1,065
Liabilities
Derivatives	0	0
Short sales	0	0
Total liabilities measured at fair value	0	0
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Debt Securities [Member]
Assets
Investments	1,397	1,065
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Equity securities [Member]
Assets
Investments	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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