Investment Securities - Fair value of investment securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair value of investments
Cash equivalents	$ 26,918	$ 42,346
Available for sale securities	222,478	256,268
Trading debt securities	172,384	180,715
Equity securities	179,879	214,176
Total investment securities	605,780	688,346
Money market funds
Fair value of investments
Cash equivalents	7,759	4,203
Commercial paper
Fair value of investments
Cash equivalents	19,159	38,143
Available for sale securities		1,977
Trading debt securities	9,573	1,977
Corporate bonds
Fair value of investments
Available for sale securities	222,478	254,291
Trading debt securities	77,325	84,920
U.S. treasury bills
Fair value of investments
Trading debt securities	6,022	5,979
Mortgage-backed securities
Fair value of investments
Trading debt securities	3	4
Term loans
Fair value of investments
Trading debt securities	37,220	44,268
Consolidated Sponsored Funds
Fair value of investments
Trading debt securities	42,241	43,567
Common Stock
Fair value of investments
Equity securities	30,528	34,945
Sponsored funds
Fair value of investments
Equity securities	148,683	178,386
Equity method securities	31,039	37,187
Sponsored privately offered funds
Fair value of investments
Equity securities	668	845
Level 1
Fair value of investments
Cash equivalents	7,759	4,203
Total investment securities	210,250	250,515
Level 1 \| Money market funds
Fair value of investments
Cash equivalents	7,759	4,203
Level 1 \| Common Stock
Fair value of investments
Equity securities	30,528	34,942
Level 1 \| Sponsored funds
Fair value of investments
Equity securities	148,683	178,386
Equity method securities	31,039	37,187
Level 2
Fair value of investments
Cash equivalents	19,159	38,143
Total investment securities	386,732	433,083
Level 2 \| Commercial paper
Fair value of investments
Cash equivalents	19,159	38,143
Available for sale securities		1,977
Trading debt securities	9,573	1,977
Level 2 \| Corporate bonds
Fair value of investments
Available for sale securities	222,478	254,291
Trading debt securities	77,325	84,920
Level 2 \| U.S. treasury bills
Fair value of investments
Trading debt securities	6,022	5,979
Level 2 \| Mortgage-backed securities
Fair value of investments
Trading debt securities	3	4
Level 2 \| Term loans
Fair value of investments
Trading debt securities	29,090	40,368
Level 2 \| Consolidated Sponsored Funds
Fair value of investments
Trading debt securities	42,241	43,567
Level 3
Fair value of investments
Total investment securities	8,130	3,903
Level 3 \| Term loans
Fair value of investments
Trading debt securities	8,130	3,900
Level 3 \| Common Stock
Fair value of investments
Equity securities		3
Other Assets Held at Net Value
Fair value of investments
Total investment securities	668	845
Other Assets Held at Net Value \| Sponsored privately offered funds
Fair value of investments
Equity securities	$ 668	$ 845

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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