Investment Securities - Fair value of investment securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair value of investments
Cash equivalents	$ 129,506	$ 42,346
Available for sale securities	167,537	256,268
Trading debt securities	135,744	180,715
Equity securities	123,594	214,176
Total investment securities	486,765	688,346
Money market funds
Fair value of investments
Cash equivalents	82,085	4,203
Commercial paper
Fair value of investments
Cash equivalents	47,421	38,143
Available for sale securities	9,705	1,977
Trading debt securities	11,785	1,977
Corporate bonds
Fair value of investments
Available for sale securities	157,832	254,291
Trading debt securities	76,734	84,920
U.S. treasury bills
Fair value of investments
Trading debt securities		5,979
Mortgage-backed securities
Fair value of investments
Trading debt securities	1	4
Term loans
Fair value of investments
Trading debt securities	47,224	44,268
Consolidated Sponsored Funds
Fair value of investments
Trading debt securities		43,567
Common Stock
Fair value of investments
Equity securities	41,410	34,945
Sponsored funds
Fair value of investments
Equity securities	81,019	178,386
Equity method securities	59,890	37,187
Sponsored privately offered funds
Fair value of investments
Equity securities	1,165	845
Level 1
Fair value of investments
Cash equivalents	82,085	4,203
Total investment securities	181,988	250,515
Level 1 \| Money market funds
Fair value of investments
Cash equivalents	82,085	4,203
Level 1 \| Common Stock
Fair value of investments
Equity securities	41,079	34,942
Level 1 \| Sponsored funds
Fair value of investments
Equity securities	81,019	178,386
Equity method securities	59,890	37,187
Level 2
Fair value of investments
Cash equivalents	47,421	38,143
Total investment securities	302,087	433,083
Level 2 \| Commercial paper
Fair value of investments
Cash equivalents	47,421	38,143
Available for sale securities	9,705	1,977
Trading debt securities	11,785	1,977
Level 2 \| Corporate bonds
Fair value of investments
Available for sale securities	157,832	254,291
Trading debt securities	76,734	84,920
Level 2 \| U.S. treasury bills
Fair value of investments
Trading debt securities		5,979
Level 2 \| Mortgage-backed securities
Fair value of investments
Trading debt securities	1	4
Level 2 \| Term loans
Fair value of investments
Trading debt securities	46,030	40,368
Level 2 \| Consolidated Sponsored Funds
Fair value of investments
Trading debt securities		43,567
Level 3
Fair value of investments
Total investment securities	1,525	3,903
Level 3 \| Term loans
Fair value of investments
Trading debt securities	1,194	3,900
Level 3 \| Common Stock
Fair value of investments
Equity securities	331	3
Other Assets Held at Net Value
Fair value of investments
Total investment securities	1,165	845
Other Assets Held at Net Value \| Sponsored privately offered funds
Fair value of investments
Equity securities	$ 1,165	$ 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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