Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available for sale securities:
Available for sale securities	$ 206,334	$ 265,198
Available for sale securities		265,198
Trading debt securities
Trading debt securities	123,818	124,390
Equity securities:
Equity securities	217,557	215,716
Equity method securities
Total investment securities	642,237	700,492
Available for sale securities	206,334	265,198
Certificates of deposit
Available for sale securities:
Available for sale securities	7,998	12,999
Trading debt securities
Trading debt securities	1,998	1,999
Equity method securities
Available for sale securities	7,998	12,999
Commercial paper
Available for sale securities:
Available for sale securities		34,978
Equity method securities
Available for sale securities		34,978
Corporate bonds
Available for sale securities:
Available for sale securities	178,719	197,442
Trading debt securities
Trading debt securities	54,833	55,414
Equity method securities
Available for sale securities	178,719	197,442
U.S. treasury bills
Available for sale securities:
Available for sale securities	19,617	19,779
Trading debt securities
Trading debt securities	4,885	4,929
Equity method securities
Available for sale securities	19,617	19,779
Mortgage-backed securities
Trading debt securities
Trading debt securities	9	10
Common stock
Equity securities:
Equity securities	130	116
Consolidated Sponsored Funds
Trading debt securities
Trading debt securities	62,093	62,038
Equity securities:
Equity securities	79,409	77,048
Sponsored funds
Equity securities:
Equity securities	137,290	137,857
Equity method securities
Equity method securities	94,528	95,188
Sponsored privately offered funds
Equity securities:
Equity securities	$ 728	$ 695

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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