Fair Value Measurements - Classes of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial Assets
Cash and Cash Equivalents	$ 116,943	$ 316,264
Investments—Consolidated Investment Companies
Equity Securities	2,101	6,170
Debt Securities	29,636	39,241
Investments—Affiliates and Other
Equity Securities	5,419	4,866
Debt Securities	2,960	2,997
Other	775	1,240
Total Financial Assets	157,834	370,778
Total Financial Liabilities	4,556	1,203
Level 1
Financial Assets
Cash and Cash Equivalents	116,943	205,364
Investments—Consolidated Investment Companies
Equity Securities	1,382	5,424
Debt Securities	0	0
Investments—Affiliates and Other
Equity Securities	5,092	4,564
Debt Securities	0	0
Other	592	123
Total Financial Assets	124,009	215,475
Total Financial Liabilities	7	0
Level 2
Financial Assets
Cash and Cash Equivalents	0	0
Investments—Consolidated Investment Companies
Equity Securities	719	746
Debt Securities	29,636	39,241
Investments—Affiliates and Other
Equity Securities	0	0
Debt Securities	2,960	2,997
Other	113	357
Total Financial Assets	33,428	43,341
Total Financial Liabilities	3,815	0
Level 3
Financial Assets
Cash and Cash Equivalents	0	0
Investments—Consolidated Investment Companies
Equity Securities	0	0
Debt Securities	0	0
Investments—Affiliates and Other
Equity Securities	39	0
Debt Securities	0	0
Other	70	760
Total Financial Assets	109	760
Total Financial Liabilities	734	1,203
NAV Practical Expedient
Financial Assets
NAV Practical Expedient	288	111,202
Investments—Affiliates and Other
NAV Practical Expedient	288	111,202
NAV Practical Expedient \| Cash and Cash Equivalents
Financial Assets
NAV Practical Expedient	0	110,900
Investments—Affiliates and Other
NAV Practical Expedient	0	110,900
NAV Practical Expedient \| Equity
Financial Assets
NAV Practical Expedient	288	302
Investments—Affiliates and Other
NAV Practical Expedient	$ 288	$ 302

Investments - Affiliates And Other - Debt Securities, Fair Value

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Investments - Affiliates and Other- Equity Securities, Fair Value

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Investments - Consolidated Investment Companies - Debt Securities, Fair Value

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Investments - Consolidated Investment Companies - Equity Securities, Fair Value

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Investments, Fair Value Disclosure, Affiliates And Other [Abstract]

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Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
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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 financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of other assets.

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