Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available for sale securities:
Available for sale securities	$ 250,764	$ 265,198
Trading debt securities:
Trading debt securities	118,222	124,390
Equity securities:
Equity securities	200,309	215,716
Equity method securities:
Total investment securities	617,135	700,492
Certificates of deposit
Available for sale securities:
Available for sale securities	5,001	12,999
Trading debt securities:
Trading debt securities		1,999
Commercial paper
Available for sale securities:
Available for sale securities	7,970	34,978
Trading debt securities:
Trading debt securities	1,993
Corporate bonds
Available for sale securities:
Available for sale securities	218,121	197,442
Trading debt securities:
Trading debt securities	77,250	55,414
U.S. treasury bills
Available for sale securities:
Available for sale securities	19,672	19,779
Trading debt securities:
Trading debt securities	5,884	4,929
Fixed income securities: Mortgage-backed securities
Trading debt securities:
Trading debt securities	7	10
Consolidated Sponsored Funds
Trading debt securities:
Trading debt securities	33,088	62,038
Equity securities:
Equity securities	24,879	77,048
Common Stock
Equity securities:
Equity securities	21,204	116
Sponsored funds
Equity securities:
Equity securities	153,548	137,857
Equity method securities:
Equity method securities	47,840	95,188
Sponsored funds \| Previous accounting guidance
Equity method securities:
Available for sale securities		124,000
Sponsored privately offered funds
Equity securities:
Equity securities	$ 678	$ 695

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