Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash Flows From Operating Activities
Net Income	$ 120,524	$ 41,271
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Net (Gains) Losses on Investments, Marketable Securities and Contingent Consideration	1,135	198
Equity Method Investments	2,698	4,251
Equity-Based and Other Deferred Compensation	99,237	124,348
Impairment of Goodwill and Equity Method Investments	21,507	0
Depreciation, Amortization and Accretion	11,969	13,067
Bad Debt Expense	1,140	554
Deferred Taxes	(6,425)	(958)
Decrease (Increase) in Operating Assets:
Marketable Securities	367	339
Financial Instruments Owned and Pledged as Collateral at Fair Value	3,876	27,417
Securities Purchased Under Agreements to Resell	(4,674)	(20,468)
Accounts Receivable	48,588	(17,790)
Receivable from Employees and Related Parties	(1,019)	3,027
Other Assets	8,495	(7,671)
(Decrease) Increase in Operating Liabilities:
Accrued Compensation and Benefits	(128,598)	(148,263)
Accounts Payable and Accrued Expenses	(1,534)	(6,753)
Securities Sold Under Agreements to Repurchase	777	(7,011)
Payables to Employees and Related Parties	11,107	3,598
Taxes Payable	(18,266)	(6,906)
Other Liabilities	(15,739)	11,305
Net Cash Provided by Operating Activities	155,165	13,555
Cash Flows From Investing Activities
Investments Purchased	(49)	(1,529)
Distributions of Private Equity Investments	514	107
Marketable Securities:
Proceeds from Sales and Maturities	23,124	18,260
Purchases	(14,736)	(43,820)
Assets Held for Sale	0	(906)
Purchase of Furniture, Equipment and Leasehold Improvements	(16,804)	(4,732)
Net Cash Provided by (Used in) Investing Activities	(7,951)	(32,620)
Cash Flows From Financing Activities
Issuance of Noncontrolling Interests	110	885
Distributions to Noncontrolling Interests	(15,944)	(17,193)
Cash Paid for Deferred and Contingent Consideration	0	(5,050)
Short-Term Borrowing	30,000	50,000
Repayment of Short-Term Borrowing	(30,000)	(50,000)
Repayment of Subordinated Borrowings	(9,751)	(6,000)
Payment of Notes Payable - Mizuho	0	(120,000)
Issuance of Notes Payable	0	170,000
Debt Issuance Costs	0	(2,084)
Purchase of Treasury Stock and Noncontrolling Interests	(240,377)	(166,261)
Dividends - Class A Stockholders	(29,510)	(24,397)
Net Cash Provided by (Used in) Financing Activities	(295,472)	(170,100)
Effect of Exchange Rate Changes on Cash	(54)	(12,329)
Net Increase (Decrease) in Cash and Cash Equivalents	(148,312)	(201,494)
Cash and Cash Equivalents-Beginning of Period	558,524	448,764
Cash and Cash Equivalents-End of Period	410,212	247,270
SUPPLEMENTAL CASH FLOW DISCLOSURE
Payments for Interest	9,322	4,757
Payments for Income Taxes	66,963	50,131
Accrued Dividends	4,714	3,870
Settlement of Contingent Consideration	$ 10,780	$ 0