Investment Securities - Fair value of investment securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair value of investments
Cash equivalents	$ 41,090	$ 196,931
Available for sale securities	269,039	250,764
Trading debt securities	180,546	118,222
Equity securities	206,744	200,309
Total investment securities	691,616	617,135
Money market funds
Fair value of investments
Cash equivalents	3,090	121,759
U.S. government sponsored enterprise note
Fair value of investments
Cash equivalents	896	895
Certificates of deposit
Fair value of investments
Available for sale securities		5,001
Commercial paper
Fair value of investments
Cash equivalents	37,104	74,277
Available for sale securities	1,975	7,970
Trading debt securities	1,975	1,993
Corporate bonds
Fair value of investments
Available for sale securities	267,064	218,121
Trading debt securities	89,057	77,250
U.S. treasury bills
Fair value of investments
Available for sale securities		19,672
Trading debt securities	5,968	5,884
Mortgage-backed securities
Fair value of investments
Trading debt securities	5	7
Term loans
Fair value of investments
Trading debt securities	42,272
Common Stock
Fair value of investments
Equity securities	31,744	21,204
Consolidated Sponsored Funds
Fair value of investments
Trading debt securities	41,269	33,088
Equity securities		24,879
Sponsored funds
Fair value of investments
Equity securities	174,219	153,548
Equity method securities	35,287	47,840
Sponsored privately offered funds
Fair value of investments
Equity securities	781	678
Level 1
Fair value of investments
Cash equivalents	3,090	121,759
Total investment securities	241,248	247,459
Level 1 \| Money market funds
Fair value of investments
Cash equivalents	3,090	121,759
Level 1 \| Common Stock
Fair value of investments
Equity securities	31,742	21,192
Level 1 \| Consolidated Sponsored Funds
Fair value of investments
Equity securities		24,879
Level 1 \| Sponsored funds
Fair value of investments
Equity securities	174,219	153,548
Equity method securities	35,287	47,840
Level 2
Fair value of investments
Cash equivalents	38,000	75,172
Total investment securities	448,192	368,986
Level 2 \| U.S. government sponsored enterprise note
Fair value of investments
Cash equivalents	896	895
Level 2 \| Certificates of deposit
Fair value of investments
Available for sale securities		5,001
Level 2 \| Commercial paper
Fair value of investments
Cash equivalents	37,104	74,277
Available for sale securities	1,975	7,970
Trading debt securities	1,975	1,993
Level 2 \| Corporate bonds
Fair value of investments
Available for sale securities	267,064	218,121
Trading debt securities	89,057	77,250
Level 2 \| U.S. treasury bills
Fair value of investments
Available for sale securities		19,672
Trading debt securities	5,968	5,884
Level 2 \| Mortgage-backed securities
Fair value of investments
Trading debt securities	5	7
Level 2 \| Term loans
Fair value of investments
Trading debt securities	40,879
Level 2 \| Consolidated Sponsored Funds
Fair value of investments
Trading debt securities	41,269	33,088
Level 3
Fair value of investments
Total investment securities	1,395	12
Level 3 \| Term loans
Fair value of investments
Trading debt securities	1,393
Level 3 \| Common Stock
Fair value of investments
Equity securities	2	12
Other Assets Held at Net Value
Fair value of investments
Total investment securities	781	678
Other Assets Held at Net Value \| Sponsored privately offered funds
Fair value of investments
Equity securities	$ 781	$ 678

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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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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No definition available.

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Amount of investment in marketable security, classified as current.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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