Consolidation - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets
Cash equivalents	$ 28,617	$ 54,772
Total assets measured at fair value	113,441	101,578
Level 1 [Member]
Assets
Cash equivalents	28,617	54,772
Total assets measured at fair value	113,441	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	64	771
Total assets measured at fair value	199,694	324,106
Liabilities
Derivatives	81	972
Short sales	1,495	5,409
Total liabilities measured at fair value	1,576	6,381
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Debt Securities [Member]
Assets
Investments	125,018	152,553
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Assets
Investments	74,612	170,782
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets
Derivatives	33	33
Total assets measured at fair value	74,302	163,019
Liabilities
Derivatives	0	128
Short sales	1,495	5,334
Total liabilities measured at fair value	1,495	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	74,269	162,986
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets
Derivatives	31	738
Total assets measured at fair value	124,396	159,690
Liabilities
Derivatives	81	844
Short sales	0	75
Total liabilities measured at fair value	81	919
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Debt Securities [Member]
Assets
Investments	124,341	151,156
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Equity Securities [Member]
Assets
Investments	24	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	996	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	677	1,397
Consolidated Sponsored Investment Products [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Equity Securities [Member]
Assets
Investments	319	0
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member]
Assets
Cash equivalents	7,440	8,297
Investments	193,663	199,485
Total assets measured at fair value	201,103	207,782
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets
Cash equivalents	7,440	8,297
Investments	0	0
Total assets measured at fair value	7,440	8,297
Consolidated Investment Product [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets
Cash equivalents	0	0
Investments	193,663	199,485
Total assets measured at fair value	193,663	199,485
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

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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+ References

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Fair value of obligations incurred from short sales.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value of financial and nonfinancial obligations.

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