Fair Value Measurements for Operating Entities and Consolidated Funds - Carrying Value Disclosures (Details) - USD ($)		Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Cash and cash equivalents		$ 512,978,000	$ 914,343,000	$ 1,147,531,000
Cash collateral pledged		52,865,000	47,494,000	110,303,000
Segregated Cash		220,882,000	194,701,000	168,942,000
Securities Purchased under Agreements to Resell		19,621,000	0
Securities borrowed		1,761,146,000	1,704,603,000
Loans Receivable, Net		5,041,000	4,858,000
Cash and cash equivalents, Consolidated Funds		23,000	296,000	$ 935,000
Securities Sold under Agreements to Repurchase		229,192,000	63,469,000
Securities sold under agreements to repurchase, Fair value		249,116,000	74,443,000
Securities Loaned		1,735,852,000	1,586,572,000
Long-term Debt	[1]	625,766,000	623,371,000
Notes Payable, Other Payables
Unamortized discount		2,700,000	2,800,000
Debt Instrument, Unamortized Premium		200,000	300,000
Level 1
Cash and cash equivalents, Fair Value		512,978,000	914,343,000
Segregated cash fair value disclosures		220,882,000	194,701,000
Cash and cash equivalents, Consolidated Funds, Fair Value		23,000	296,000
Level 2
Cash collateral pledged, Fair Value		52,865,000	47,494,000
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure		19,621,000	0
Securities Borrowed, Fair Value Disclosure		1,761,146,000	1,704,603,000
Securities sold under agreements to repurchase, Fair value		229,192,000	63,469,000
Securities loaned, fair value disclosure		1,735,852,000	1,586,572,000
Notes payable and other debt, Fair Value	[2]	644,238,000	655,229,000
Level 3
Loans Receivable, Fair Value Disclosure	[3]	$ 5,041,000	$ 4,858,000

[1] The carrying amount of the notes payable and other debt includes an unamortized discount and unamortized premium of $2.7 million and $0.2 million as of March 31, 2022, respectively, and unamortized discount and unamortized premium of $2.8 million and $0.3 million as of December 31, 2021, respectively.

[2] Notes payable and other debt are based on the last broker quote available.

[3] The fair market value of level 3 loans is calculated using discounted cash flows where applicable.