Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows From Operating Activities
Net Income	$ 412,680	$ 353,661	$ 442,851
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Net (Gains) Losses on Investments, Investment Securities and Contingent Consideration	(8,681)	(13,750)	10,718
Equity Method Investments	(1,636)	403	1,352
Equity-Based and Other Deferred Compensation	367,438	360,341	293,507
Net Loss on Sale and Wind-down of Operations in Mexico, Including Release of Cumulative Foreign Exchange Losses	35,247	0	0
Impairment of Goodwill	0	2,921	0
Noncash Lease Expense	38,626	29,259	0
Depreciation, Amortization and Accretion	30,002	35,730	29,374
Bad Debt Expense	6,878	10,451	3,365
Deferred Taxes	13,824	(10,503)	(3,981)
Decrease (Increase) in Operating Assets:
Investment Securities	3,559	(491)	(546)
Financial Instruments Owned and Pledged as Collateral at Fair Value	(1,516)	10,629	(2,961)
Securities Purchased Under Agreements to Resell	(399)	(10,541)	8,166
Accounts Receivable	(78,573)	5,241	(130,956)
Receivable from Employees and Related Parties	(1,170)	1,450	(6,849)
Other Assets	(19,043)	(58,962)	(21,830)
(Decrease) Increase in Operating Liabilities:
Accrued Compensation and Benefits	82,364	(180,767)	208,088
Accounts Payable and Accrued Expenses	(796)	(745)	5,496
Securities Sold Under Agreements to Repurchase	1,935	(115)	(5,183)
Payables to Employees and Related Parties	(7,980)	(599)	4,387
Taxes Payable	11,946	(30,221)	16,099
Other Liabilities	93,666	1,305	(1,523)
Net Cash Provided by Operating Activities	978,371	504,697	849,574
Cash Flows From Investing Activities
Investments Purchased	(143)	(3,843)	(95)
Distributions of Private Equity Investments	650	1,893	2,143
Investment Securities:
Proceeds from Sales and Maturities of Investment Securities and Futures Contracts Activity	555,624	510,151	191,779
Purchases of Investment Securities and Futures Contracts Activity	(1,201,617)	(698,995)	(336,596)
Maturity of Certificates of Deposit	214,266	100,000	63,527
Purchase of Certificates of Deposit	0	(211,861)	(100,000)
Purchase of Furniture, Equipment and Leasehold Improvements	(53,330)	(70,816)	(33,324)
Proceeds from Sale of Business, Net of Cash Sold	679	0	0
Net Cash Provided by (Used In) Investing Activities	(483,871)	(373,471)	(212,566)
Cash Flows From Financing Activities
Issuance of Noncontrolling Interests	540	600	1,165
Distributions to Noncontrolling Interests	(44,915)	(54,706)	(41,413)
Payments Under Tax Receivable Agreement	(9,425)	(9,490)	(13,345)
Short-Term Borrowings	0	30,000	30,000
Repayment of Short-Term Borrowings	0	(30,000)	(30,000)
Repayment of Subordinated Borrowings	0	0	(6,799)
Issuance of Notes Payable	0	205,718	0
Debt Issuance Costs	0	(2,032)	0
Purchase of Treasury Stock and Noncontrolling Interests	(147,411)	(333,296)	(315,233)
Dividends	(106,582)	(96,803)	(77,302)
Net Cash Provided by (Used in) Financing Activities	(307,793)	(290,009)	(452,927)
Effect of Exchange Rate Changes on Cash	7,631	2,573	(1,370)
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash	194,338	(156,210)	182,711
Cash, Cash Equivalents and Restricted Cash-Beginning of Period	643,886	800,096	617,385
Cash, Cash Equivalents and Restricted Cash-End of Period	838,224	643,886	800,096
SUPPLEMENTAL CASH FLOW DISCLOSURE
Payments for Interest	23,748	16,405	17,818
Payments for Income Taxes	111,319	155,478	86,232
Accrued Dividends	13,734	14,642	12,288
Noncash Purchase of Noncontrolling Interest	$ 851	$ 2,701	$ 0