Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows From Operating Activities
Net Income	$ 107,371	$ 72,022	$ 39,479
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Net (Gains) Losses on Investments, Marketable Securities and Contingent Consideration	(2,505)	(2,172)	756
Equity Method Investments	4,476	(1,454)	(2,672)
Equity-Based and Other Deferred Compensation	111,771	121,608	115,632
Depreciation, Amortization and Accretion	18,773	16,699	18,784
Bad Debt Expense	1,027	2,099	1,803
Adjustment to Tax Receivable Agreements	0	(6,905)	0
Deferred Taxes	14,315	20,058	(7,967)
Decrease (Increase) in Operating Assets:
Marketable Securities	550	234	674
Financial Instruments Owned and Pledged as Collateral at Fair Value	(54,032)	65,045	16,056
Securities Purchased Under Agreements to Resell	10,303	(19,578)	2,278
Accounts Receivable	(51,166)	1,460	(37,111)
Receivable from Employees and Related Parties	(6,646)	(4,542)	2,627
Other Assets	(7,651)	(19,945)	15,485
(Decrease) Increase in Operating Liabilities:
Accrued Compensation and Benefits	27,251	12,435	2,967
Accounts Payable and Accrued Expenses	6,231	258	466
Securities Sold Under Agreements to Repurchase	43,771	(45,543)	(18,413)
Payables to Employees and Related Parties	(2,601)	4,451	(2,429)
Taxes Payable	(2,650)	(15,591)	13,694
Other Liabilities	(2,616)	(1,925)	(1,951)
Net Cash Provided by Operating Activities	215,972	198,714	160,158
Cash Flows From Investing Activities
Investments Purchased	(10,944)	(3,012)	(2,161)
Distributions of Private Equity Investments	672	1,300	1,192
Marketable Securities:
Proceeds from Sales and Maturities	34,719	31,106	67,958
Purchases	(28,760)	(35,187)	(23,499)
Cash Acquired for Acquisitions, net of Cash Paid	42,869	218	(6,743)
Proceeds from Sale of Business	0	1,198	0
Change in Restricted Cash	0	0	2,111
Purchase of Furniture, Equipment and Leasehold Improvements	(13,521)	(4,487)	(13,941)
Net Cash Provided by (Used in) Investing Activities	25,035	(8,864)	24,917
Cash Flows From Financing Activities
Payments for Settlement of Debt and Capital Lease Obligations	0	0	(1,047)
Issuance of Noncontrolling Interests	2,135	3,589	469
Distributions to Noncontrolling Interests	(10,655)	(18,950)	(16,528)
Payments Under Tax Receivable Agreement	(9,086)	(7,651)	0
Cash Paid for Deferred and Contingent Consideration	(2,255)	(3,396)	(3,000)
Short-Term Borrowing	75,000	0	0
Repayment of Short-Term Borrowing	(75,000)	0	0
Purchase of Treasury Stock and Noncontrolling Interests	(156,242)	(102,277)	(66,983)
Excess Tax Benefits Associated with Equity-Based Awards	35,262	8,979	1,451
Dividends - Class A Stockholders	(38,754)	(30,090)	(24,296)
Other	0	0	(78)
Net Cash Provided by (Used in) Financing Activities	(179,595)	(149,796)	(110,012)
Effect of Exchange Rate Changes on Cash	(7,705)	(1,032)	1,463
Net Increase in Cash and Cash Equivalents	53,707	39,022	76,526
Cash and Cash Equivalents-Beginning of Period	298,453	259,431	182,905
Cash and Cash Equivalents-End of Period	352,160	298,453	259,431
SUPPLEMENTAL CASH FLOW DISCLOSURE
Payments for Interest	13,725	12,807	13,962
Payments for Income Taxes	18,283	57,178	9,569
Furniture, Equipment and Leasehold Improvements Accrued	213	1,060	267
Increase (Decrease) in Fair Value of Redeemable Noncontrolling Interest	3,261	(12,985)	27,376
Dividend Equivalents Issued	6,038	5,989	4,969
Notes Exchanged for Equity in Subsidiary	0	1,042	0
Settlement of Contingent Consideration	7,232	2,494	0
Receipt of Marketable Securities in Settlement of Accounts Receivable	2,083	2,278	0
Purchase of Noncontrolling Interest	7,100	0	0
Contingent Consideration Accrued	1,979	0	0
Reclassification from Redeemable Noncontrolling Interest to Noncontrolling Interest	27,477	0	(3,606)
Shares and LP Units Issued as Consideration for Acquisitions and Investments	79,576	0	0
Noncash or Part Noncash Acquisition, Value of Assets Acquired	106,848	0	11,931
Noncash or Part Noncash Acquisition, Value of Liabilities Assumed	$ 64,864	$ 0	$ 1,678