Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available for sale securities:
Available for sale securities	$ 222,478	$ 256,268
Trading debt securities:
Trading debt securities	172,384	180,715
Equity securities:
Equity securities	179,879	214,176
Equity method securities:
Total investment securities	605,780	688,346
Commercial paper
Available for sale securities:
Available for sale securities		1,977
Trading debt securities:
Trading debt securities	9,573	1,977
Corporate bonds
Available for sale securities:
Available for sale securities	222,478	254,291
Trading debt securities:
Trading debt securities	77,325	84,920
U.S. treasury bills
Trading debt securities:
Trading debt securities	6,022	5,979
Mortgage-backed securities
Trading debt securities:
Trading debt securities	3	4
Term loans
Trading debt securities:
Trading debt securities	37,220	44,268
Consolidated Sponsored Funds
Trading debt securities:
Trading debt securities	42,241	43,567
Common Stock
Equity securities:
Equity securities	30,528	34,945
Sponsored funds
Equity securities:
Equity securities	148,683	178,386
Equity method securities:
Equity method securities	31,039	37,187
Sponsored privately offered funds
Equity securities:
Equity securities	$ 668	$ 845

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