Fair Value Measurements - Changes in Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Cash equivalents	$ 207,101	$ 187,255
Investment securities - fair value
Fair Value	39,990	60,990
Total assets measured at fair value	257,703	256,969
Sponsored funds
Investment securities - fair value
Fair Value	25,909	47,654
Equity securities
Investment securities - fair value
Fair Value	14,078	13,320
Debt securities
Investment securities - fair value
Fair Value	3	16
Nonqualified retirement plan assets
Investment securities - fair value
Nonqualified retirement plan assets	10,612	8,724
Level 1
Assets
Cash equivalents	207,101	187,255
Investment securities - fair value
Total assets measured at fair value	257,700	256,953
Level 1 \| Sponsored funds
Investment securities - fair value
Fair Value	25,909	47,654
Level 1 \| Equity securities
Investment securities - fair value
Fair Value	14,078	13,320
Level 1 \| Debt securities
Investment securities - fair value
Fair Value	0	0
Level 1 \| Nonqualified retirement plan assets
Investment securities - fair value
Nonqualified retirement plan assets	10,612	8,724
Level 2
Assets
Cash equivalents	0	0
Investment securities - fair value
Total assets measured at fair value	3	16
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 \| Debt securities
Investment securities - fair value
Fair Value	3	16
Level 2 \| Nonqualified retirement plan assets
Investment securities - fair value
Nonqualified retirement plan assets	0	0
Level 3
Assets
Cash equivalents	0	0
Investment securities - fair value
Total assets measured at fair value	0	0
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 \| Debt securities
Investment securities - fair value
Fair Value	0	0
Level 3 \| Nonqualified retirement plan assets
Investment securities - fair value
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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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
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Investments In Nonqualified Retirement Plan Assets

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