Consolidation - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets
Cash equivalents	$ 223,087	$ 48,620
Total assets measured at fair value	299,868	129,335
Level 1
Assets
Cash equivalents	223,087	48,620
Total assets measured at fair value	299,868	129,335
Level 2
Assets
Cash equivalents	0	0
Total assets measured at fair value	0	0
Level 3
Assets
Cash equivalents	0	0
Total assets measured at fair value	0	0
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring
Assets
Derivatives		4
Total assets measured at fair value	112,930	142,079
Liabilities
Derivatives	281	300
Short sales	588	649
Total liabilities measured at fair value	869	949
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Debt securities
Assets
Investments	72,093	101,597
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Equity securities
Assets
Investments	40,837	40,478
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 1
Assets
Derivatives		4
Total assets measured at fair value	40,470	40,274
Liabilities
Derivatives	1	3
Short sales	588	649
Total liabilities measured at fair value	589	652
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 1 \| Debt securities
Assets
Investments	0	0
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 1 \| Equity securities
Assets
Investments	40,470	40,270
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 2
Assets
Derivatives		0
Total assets measured at fair value	72,299	101,718
Liabilities
Derivatives	280	235
Short sales	0	0
Total liabilities measured at fair value	280	235
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 2 \| Debt securities
Assets
Investments	71,932	101,510
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 2 \| Equity securities
Assets
Investments	367	208
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 3
Assets
Derivatives		0
Total assets measured at fair value	161	87
Liabilities
Derivatives	0	62
Short sales	0	0
Total liabilities measured at fair value	0	62
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 3 \| Debt securities
Assets
Investments	161	87
Consolidated Sponsored Investment Products \| Fair Value, Measurements, Recurring \| Level 3 \| Equity securities
Assets
Investments	0	0
Consolidated Investment Product \| Fair Value, Measurements, Recurring
Assets
Cash equivalents	13,957	14,449
Investments	354,002	346,967
Total assets measured at fair value	367,959	361,416
Liabilities
Notes payable	325,843	328,761
Total liabilities measured at fair value	325,843	328,761
Consolidated Investment Product \| Fair Value, Measurements, Recurring \| Level 1
Assets
Cash equivalents	13,957	14,449
Investments	0	0
Total assets measured at fair value	13,957	14,449
Liabilities
Notes payable	0	0
Total liabilities measured at fair value	0	0
Consolidated Investment Product \| Fair Value, Measurements, Recurring \| Level 2
Assets
Cash equivalents	0	0
Investments	352,440	346,967
Total assets measured at fair value	352,440	346,967
Liabilities
Notes payable	325,843	328,761
Total liabilities measured at fair value	325,843	328,761
Consolidated Investment Product \| Fair Value, Measurements, Recurring \| Level 3
Assets
Cash equivalents	0	0
Investments	1,562	0
Total assets measured at fair value	1,562	0
Liabilities
Notes payable	0	0
Total liabilities 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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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, 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.

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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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