Fair Value Measurements - Changes in Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents	$ 187,255	$ 158,596
Investment securities - fair value
Fair Value	60,990	59,271
Fair Value	16	2,099
Other Investments [Abstract]
Total assets measured at fair value	256,969	226,606
Sponsored funds
Investment securities - fair value
Fair Value	47,654	40,191
Equity securities
Investment securities - fair value
Fair Value	13,320	16,981
Debt securities
Investment securities - fair value
Fair Value	16	2,099
Investment securities - available for sale
Investment securities - fair value
Fair Value		2,023
Other Investments [Abstract]
Investment securities - available for sale		2,023
Nonqualified retirement plan assets
Other Investments [Abstract]
Nonqualified retirement plan assets	8,724	6,716
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents	187,255	158,596
Investment securities - fair value
Fair Value	0	0
Other Investments [Abstract]
Total assets measured at fair value	256,953	222,484
Level 1 \| Sponsored funds
Investment securities - fair value
Fair Value	47,654	40,191
Level 1 \| Equity securities
Investment securities - fair value
Fair Value	13,320	16,981
Level 1 \| Investment securities - available for sale
Other Investments [Abstract]
Investment securities - available for sale		0
Level 1 \| Nonqualified retirement plan assets
Other Investments [Abstract]
Nonqualified retirement plan assets	8,724	6,716
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents	0	0
Investment securities - fair value
Fair Value	16	0
Other Investments [Abstract]
Total assets measured at fair value	16	0
Level 2 \| Sponsored funds
Investment securities - fair value
Fair Value	0	0
Level 2 \| Equity securities
Investment securities - fair value
Fair Value	0	0
Level 2 \| Investment securities - available for sale
Other Investments [Abstract]
Investment securities - available for sale		0
Level 2 \| Nonqualified retirement plan assets
Other Investments [Abstract]
Nonqualified retirement plan assets	0	0
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash equivalents	0	0
Investment securities - fair value
Fair Value	0	2,099
Other Investments [Abstract]
Total assets measured at fair value	0	4,122
Level 3 \| Sponsored funds
Investment securities - fair value
Fair Value	0	0
Level 3 \| Equity securities
Investment securities - fair value
Fair Value	0	0
Level 3 \| Investment securities - available for sale
Other Investments [Abstract]
Investment securities - available for sale		2,023
Level 3 \| Nonqualified retirement plan assets
Other Investments [Abstract]
Nonqualified retirement plan assets	$ 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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Investments In Collateralized Loan Obligations

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Investments In Nonqualified Retirement Plan Assets

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