Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash Flows From Operating Activities
Net Income	$ 191,396	$ 120,524
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Net (Gains) Losses on Investments, Marketable Securities and Contingent Consideration	1,941	1,135
Equity Method Investments	3,673	2,698
Equity-Based and Other Deferred Compensation	141,225	99,237
Impairment of Goodwill and Equity Method Investments	0	21,507
Depreciation, Amortization and Accretion	13,523	11,969
Bad Debt Expense	1,622	1,140
Deferred Taxes	(1,576)	(6,425)
Decrease (Increase) in Operating Assets:
Marketable Securities	36	367
Financial Instruments Owned and Pledged as Collateral at Fair Value	508	3,876
Securities Purchased Under Agreements to Resell	(50)	(4,674)
Accounts Receivable	(92,014)	48,588
Receivable from Employees and Related Parties	(4,075)	(1,019)
Other Assets	(4,401)	9,134
(Decrease) Increase in Operating Liabilities:
Accrued Compensation and Benefits	(81,922)	(128,598)
Accounts Payable and Accrued Expenses	6,506	(1,534)
Securities Sold Under Agreements to Repurchase	(447)	777
Payables to Employees and Related Parties	13,415	11,107
Taxes Payable	(11,125)	(18,266)
Other Liabilities	(3,728)	(15,739)
Net Cash Provided by Operating Activities	174,507	155,804
Cash Flows From Investing Activities
Investments Purchased	(45)	(49)
Distributions of Private Equity Investments	1,578	514
Marketable Securities:
Proceeds from Sales and Maturities	41,950	23,124
Purchases	(176,202)	(14,736)
Maturity of Certificates of Deposit	63,527	0
Purchase of Certificates of Deposit	(50,000)	0
Purchase of Furniture, Equipment and Leasehold Improvements	(7,178)	(16,804)
Net Cash Provided by (Used in) Investing Activities	(126,370)	(7,951)
Cash Flows From Financing Activities
Issuance of Noncontrolling Interests	830	110
Distributions to Noncontrolling Interests	(20,584)	(15,944)
Short-Term Borrowing	30,000	30,000
Repayment of Short-Term Borrowing	(30,000)	(30,000)
Repayment of Subordinated Borrowings	(6,799)	(9,751)
Purchase of Treasury Stock and Noncontrolling Interests	(185,373)	(240,377)
Dividends - Class A Stockholders	(37,019)	(29,510)
Net Cash Provided by (Used in) Financing Activities	(248,945)	(295,472)
Effect of Exchange Rate Changes on Cash	(1,576)	(54)
Net Increase (Decrease) in Cash, Cash Equivalents and Restricted Cash	(202,384)	(147,673)
Cash, Cash Equivalents and Restricted Cash-Beginning of Period	617,385	575,637
Cash, Cash Equivalents and Restricted Cash-End of Period	415,001	427,964
SUPPLEMENTAL CASH FLOW DISCLOSURE
Payments for Interest	9,636	9,322
Payments for Income Taxes	32,796	66,963
Accrued Dividends	5,869	4,714
Settlement of Contingent Consideration	$ 0	$ 10,780