Consolidation - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets
Cash equivalents	$ 138,303	$ 54,772
Total assets measured at fair value	225,451	101,578
Level 1 [Member]
Assets
Cash equivalents	138,303	54,772
Total assets measured at fair value	225,451	101,578
Level 2 [Member]
Assets
Cash equivalents	0	0
Total assets measured at fair value	0	0
Level 3 [Member]
Assets
Cash equivalents	0	0
Total assets measured at fair value	0	0
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member]
Assets
Derivatives	6	771
Total assets measured at fair value	137,146	324,106
Liabilities
Derivatives	188	972
Short sales	522	5,409
Total liabilities measured at fair value	710	6,381
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Debt Securities [Member]
Assets
Investments	98,873	152,553
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Assets
Investments	38,267	170,782
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets
Derivatives	0	33
Total assets measured at fair value	33,524	163,019
Liabilities
Derivatives	0	128
Short sales	522	5,334
Total liabilities measured at fair value	522	5,462
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	33,524	162,986
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets
Derivatives	6	738
Total assets measured at fair value	103,476	159,690
Liabilities
Derivatives	188	844
Short sales	0	75
Total liabilities measured at fair value	188	919
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Debt Securities [Member]
Assets
Investments	98,727	151,156
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member]
Assets
Investments	4,743	7,796
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets
Derivatives	0	0
Total assets measured at fair value	146	1,397
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	146	1,397
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Equity Securities [Member]
Assets
Investments	0	0
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member]
Assets
Cash equivalents	12,703	8,297
Investments	360,210	199,485
Total assets measured at fair value	372,913	207,782
Liabilities
Notes payable	323,852
Total liabilities measured at fair value	323,852
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets
Cash equivalents	12,703	8,297
Investments	0	0
Total assets measured at fair value	12,703	8,297
Liabilities
Notes payable	0
Total liabilities measured at fair value	0
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets
Cash equivalents	0	0
Investments	360,210	199,485
Total assets measured at fair value	360,210	199,485
Liabilities
Notes payable	323,852
Total liabilities measured at fair value	323,852
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets
Cash equivalents	0	0
Investments	0	0
Total assets measured at fair value	0	$ 0
Liabilities
Notes payable	0
Total liabilities measured at fair value	$ 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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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of obligations incurred from short sales.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of notes payable.

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