Investment Securities - Fair value of investment securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair value of investments
Cash equivalents	$ 83,101	$ 42,346
Available for sale securities	206,527	256,268
Trading debt securities	186,697	180,715
Equity securities	184,420	214,176
Total investment securities	619,052	688,346
Money market funds
Fair value of investments
Cash equivalents	54,598	4,203
Commercial paper
Fair value of investments
Cash equivalents	28,503	38,143
Available for sale securities	2,728	1,977
Trading debt securities	12,502	1,977
Corporate bonds
Fair value of investments
Available for sale securities	203,799	254,291
Trading debt securities	79,136	84,920
U.S. treasury bills
Fair value of investments
Trading debt securities	6,001	5,979
Mortgage-backed securities
Fair value of investments
Trading debt securities	2	4
Term loans
Fair value of investments
Trading debt securities	39,643	44,268
Consolidated Sponsored Funds
Fair value of investments
Trading debt securities	49,413	43,567
Common Stock
Fair value of investments
Equity securities	39,252	34,945
Sponsored funds
Fair value of investments
Equity securities	144,320	178,386
Equity method securities	41,408	37,187
Sponsored privately offered funds
Fair value of investments
Equity securities	848	845
Level 1
Fair value of investments
Cash equivalents	54,598	4,203
Total investment securities	224,980	250,515
Level 1 \| Money market funds
Fair value of investments
Cash equivalents	54,598	4,203
Level 1 \| Common Stock
Fair value of investments
Equity securities	39,252	34,942
Level 1 \| Sponsored funds
Fair value of investments
Equity securities	144,320	178,386
Equity method securities	41,408	37,187
Level 2
Fair value of investments
Cash equivalents	28,503	38,143
Total investment securities	389,571	433,083
Level 2 \| Commercial paper
Fair value of investments
Cash equivalents	28,503	38,143
Available for sale securities	2,728	1,977
Trading debt securities	12,502	1,977
Level 2 \| Corporate bonds
Fair value of investments
Available for sale securities	203,799	254,291
Trading debt securities	79,136	84,920
Level 2 \| U.S. treasury bills
Fair value of investments
Trading debt securities	6,001	5,979
Level 2 \| Mortgage-backed securities
Fair value of investments
Trading debt securities	2	4
Level 2 \| Term loans
Fair value of investments
Trading debt securities	35,990	40,368
Level 2 \| Consolidated Sponsored Funds
Fair value of investments
Trading debt securities	49,413	43,567
Level 3
Fair value of investments
Total investment securities	3,653	3,903
Level 3 \| Term loans
Fair value of investments
Trading debt securities	3,653	3,900
Level 3 \| Common Stock
Fair value of investments
Equity securities		3
Other Assets Held at Net Value
Fair value of investments
Total investment securities	848	845
Other Assets Held at Net Value \| Sponsored privately offered funds
Fair value of investments
Equity securities	$ 848	$ 845

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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