Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available for sale securities:
Available for sale securities	$ 269,039	$ 250,764
Trading debt securities:
Trading debt securities	180,546	118,222
Equity securities:
Equity securities	206,744	200,309
Equity method securities:
Total investment securities	691,616	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	1,975	7,970
Trading debt securities:
Trading debt securities	1,975	1,993
Corporate bonds
Available for sale securities:
Available for sale securities	267,064	218,121
Trading debt securities:
Trading debt securities	89,057	77,250
U.S. treasury bills
Available for sale securities:
Available for sale securities		19,672
Trading debt securities:
Trading debt securities	5,968	5,884
Mortgage-backed securities
Trading debt securities:
Trading debt securities	5	7
Term loans
Trading debt securities:
Trading debt securities	42,272
Consolidated Sponsored Funds
Trading debt securities:
Trading debt securities	41,269	33,088
Equity securities:
Equity securities		24,879
Common Stock
Equity securities:
Equity securities	31,744	21,204
Sponsored funds
Equity securities:
Equity securities	174,219	153,548
Equity method securities:
Equity method securities	35,287	47,840
Sponsored privately offered funds
Equity securities:
Equity securities	$ 781	$ 678

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