Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Consolidated net income (loss)	$ 111,120	$ 95,826
Adjustments to reconcile consolidated net income (loss) to net cash provided by operating activities:
Fixed asset depreciation and intangible asset amortization	56,865	62,428
Employee loan amortization and reserves on employee loans	44,656	30,861
Equity-based compensation and allocations of net income to limited partnership units and FPUs	150,023	128,827
Deferred compensation expense	13,287	17,615
Losses (gains) on equity method investments	(1,741)	(2,678)
Amortization of discount (premium) on notes payable	(2,414)	4,427
Unrealized loss (gain) on marketable securities	(973)	(5,286)
Impairment of fixed assets	3,737	18,800
Deferred tax provision (benefit)	(57,915)	7,518
Sublease provision adjustment	(807)	(1,385)
Recognition of earn-out and related hedges	(67,016)	(52,917)
Realized losses (gains) on marketable securities (see Note 9- "Marketable Securities")	(11,792)	(31,757)
Change in the fair value of contingent consideration	(18,347)
Loss (gain) on sale of cost method investment	(7,051)
Loss (gain) on divestitures		(537)
Forfeitures of Class A common stock	(374)	(1,376)
Other	(391)	(1,750)
Consolidated net income (loss), adjusted for non-cash and non-operating items	210,867	268,616
Decrease (increase) in operating assets:
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	(948,476)	153,851
Loans, forgivable loans and other receivables from employees and partners, net	(140,201)	(56,142)
Accrued commissions receivable, net	(19,632)	25,229
Securities borrowed		62,736
Securities owned	(179,695)	2,106
Receivables from related parties	13,544	(3,752)
Cash segregated under regulatory requirements	(3,704)	6,995
Other assets	9,166	24,963
Increase (decrease) in operating liabilities:
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	897,494	(211,459)
Payables to related parties	(4,795)	9,897
Securities sold, not yet purchased		(1,526)
Securities loaned	(117,967)	54,731
Accounts payable, accrued and other liabilities	67,093	(108,178)
Accrued compensation	(31,685)	(101,507)
Net cash provided by (used in) operating activities	(247,991)	126,560
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of fixed assets	(36,844)	(26,816)
Capitalization of software development costs	(17,595)	(12,470)
Purchase of equity method investments	(7,612)	(981)
Payments for acquisitions, net of cash acquired	(119,212)	(170,792)
Purchase of marketable securities	(68,396)
Proceeds from sale of marketable securities	618,090	1,922
Proceeds from sale of cost method investments	7,106
Disposal of assets and liabilities held for sale, net		(5,633)
Capitalization of trademarks, patent defense and registration costs	(420)	(744)
Net cash provided by (used in) investing activities	375,117	(215,514)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments of collateralized borrowings	(5,121)	(3,302)
Repayments of convertible notes	(159,932)
Issuance of senior notes, net of deferred issuance costs	295,768
Issuance of collateralized borrowings, net of deferred issuance costs		27,918
Earnings distributions	(60,629)	(51,314)
Redemption and repurchase of limited partnership interests	(27,664)	(25,182)
Dividends to stockholders	(126,318)	(96,087)
Repurchase of Class A common stock	(72,700)	(6,786)
Cancellation of restricted stock units in satisfaction of withholding tax requirements	(1,542)	(520)
Proceeds from issuance of Class A common stock, net of costs	15,280
Proceeds from exercise of stock options	86	627
Repayments of short-term borrowings		5,000
Net cash provided by (used in) financing activities	(142,772)	(149,646)
Cash and cash equivalents classified as assets held for sale		23,228
Effect of exchange rate changes on cash and cash equivalents	2,954	(8,515)
Net increase (decrease) in cash and cash equivalents	(12,692)	(223,887)
Cash and cash equivalents at beginning of period	461,207	648,277
Cash and cash equivalents at end of period	448,515	424,390
Supplemental cash information:
Cash paid during the period for taxes	55,196	19,438
Cash paid during the period for interest	45,169	45,956
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests	53,754	52,521
Issuance of Class A and contingent Class A common stock for acquisitions	5,857	35,062
Issuance of Class A common stock upon conversion of convertible notes	68	150,000
Nasdaq [Member]
Supplemental non-cash information:
Shares received for Nasdaq earn-out	$ 67,016	$ 52,917