Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash Flows From Operating Activities
Net Income	$ 38,880,000	$ 78,200,000
Adjustments to Reconcile Net Income to Net Cash Provided by (Used In) Operating Activities:
Net (Gains) Losses on Investments, Investment Securities and Contingent Consideration	24,767,000	(6,207,000)
Equity Method Investments	(1,291,000)	(910,000)
Equity-Based and Other Deferred Compensation	77,910,000	96,951,000
Noncash Lease Expense	9,065,000	8,479,000
Depreciation, Amortization and Accretion	8,526,000	8,135,000
Bad Debt Expense	474,000	1,353,000
Deferred Taxes	2,105,000	(6,598,000)
Decrease (Increase) in Operating Assets:
Investment Securities	634,000	(49,000)
Financial Instruments Owned and Pledged as Collateral at Fair Value	(13,099,000)	5,741,000
Securities Purchased Under Agreements to Resell	12,831,000	(5,887,000)
Accounts Receivable	42,009,000	(47,194,000)
Receivable from Employees and Related Parties	(2,344,000)	1,654,000
Other Assets	(11,564,000)	(3,382,000)
(Decrease) Increase in Operating Liabilities:
Accrued Compensation and Benefits	(359,947,000)	(519,492,000)
Accounts Payable and Accrued Expenses	(6,070,000)	(1,257,000)
Securities Sold Under Agreements to Repurchase	266,000	119,000
Payables to Employees and Related Parties	4,152,000	13,141,000
Taxes Payable	(2,829,000)	(32,606,000)
Other Liabilities	1,219,000	(2,939,000)
Net Cash Provided (Used In) by Operating Activities	(174,306,000)	(412,748,000)
Cash Flows From Investing Activities
Investments Purchased	0	(2,440,000)
Distributions of Private Equity Investments	0	364,000
Investment Securities:
Proceeds from Sales and Maturities of Investment Securities	332,819,000	136,606,000
Purchases of Investment Securities and Futures Contracts Activity	(209,602,000)	(138,493,000)
Maturity of Certificates of Deposit	214,266,000	100,000,000
Purchase of Furniture, Equipment and Leasehold Improvements	(12,661,000)	(15,644,000)
Net Cash Provided by Investing Activities	324,822,000	80,393,000
Cash Flows From Financing Activities
Issuance of Noncontrolling Interests	30,000	0
Distributions to Noncontrolling Interests	(11,068,000)	(17,984,000)
Short-Term Borrowings	0	30,000,000
Purchase of Treasury Stock and Noncontrolling Interests	(141,014,000)	(107,693,000)
Dividends	(33,781,000)	(27,471,000)
Net Cash Provided by (Used in) Financing Activities	(185,833,000)	(123,148,000)
Effect of Exchange Rate Changes on Cash	(8,429,000)	3,868,000
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash	(43,746,000)	(451,635,000)
Cash, Cash Equivalents and Restricted Cash-Beginning of Period	643,886,000	800,096,000
Cash, Cash Equivalents and Restricted Cash-End of Period	600,140,000	348,461,000
SUPPLEMENTAL CASH FLOW DISCLOSURE
Payments for Interest	5,667,000	6,297,000
Payments for Income Taxes	20,896,000	50,736,000
Accrued Dividends	3,531,000	3,336,000
Non-Cash Purchase of Noncontrolling Interest	$ 1,703,000	$ 0