Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available for sale securities:
Available for sale securities	$ 206,527	$ 256,268
Trading debt securities:
Trading debt securities	186,697	180,715
Equity securities:
Equity securities	184,420	214,176
Equity method securities:
Total investment securities	619,052	688,346
Commercial paper
Available for sale securities:
Available for sale securities	2,728	1,977
Trading debt securities:
Trading debt securities	12,502	1,977
Corporate bonds
Available for sale securities:
Available for sale securities	203,799	254,291
Trading debt securities:
Trading debt securities	79,136	84,920
U.S. treasury bills
Trading debt securities:
Trading debt securities	6,001	5,979
Mortgage-backed securities
Trading debt securities:
Trading debt securities	2	4
Term loans
Trading debt securities:
Trading debt securities	39,643	44,268
Consolidated Sponsored Funds
Trading debt securities:
Trading debt securities	49,413	43,567
Common Stock
Equity securities:
Equity securities	39,252	34,945
Sponsored funds
Equity securities:
Equity securities	144,320	178,386
Equity method securities:
Equity method securities	41,408	37,187
Sponsored privately offered funds
Equity securities:
Equity securities	$ 848	$ 845

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