Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available for sale securities:
Available for sale securities	$ 256,268	$ 250,764
Trading debt securities:
Trading debt securities	180,715	118,222
Equity securities:
Equity securities	214,176	200,309
Equity method securities:
Total investment securities	688,346	617,135
Certificates of deposit
Available for sale securities:
Available for sale securities		5,001
Commercial paper
Available for sale securities:
Available for sale securities	1,977	7,970
Trading debt securities:
Trading debt securities	1,977	1,993
Corporate bonds
Available for sale securities:
Available for sale securities	254,291	218,121
Trading debt securities:
Trading debt securities	84,920	77,250
U.S. treasury bills
Available for sale securities:
Available for sale securities		19,672
Trading debt securities:
Trading debt securities	5,979	5,884
Mortgage-backed securities
Trading debt securities:
Trading debt securities	4	7
Term loans
Trading debt securities:
Trading debt securities	44,268
Consolidated Sponsored Funds
Trading debt securities:
Trading debt securities	43,567	33,088
Equity securities:
Equity securities		24,879
Common Stock
Equity securities:
Equity securities	34,945	21,204
Sponsored funds
Equity securities:
Equity securities	178,386	153,548
Equity method securities:
Equity method securities	37,187	47,840
Sponsored privately offered funds
Equity securities:
Equity securities	$ 845	$ 678

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