Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CASH FLOWS FROM OPERATING ACTIVITIES:
Consolidated net income	$ 38,360	$ 45,372	$ 40,813
Adjustments to reconcile net income to net cash provided by operating activities:
Fixed asset depreciation and intangible asset amortization	49,281	50,180	52,974
Employee loan amortization	31,785	41,192	34,115
Equity-based compensation	125,099	25,705	22,134
Allocations of net income to limited partnership units and founding/working partner units	18,437	23,307	16,731
Losses on equity investments	6,605	6,940	8,687
Sublease provision adjustment	4,956
Impairment loss on marketable securities	4,047
Accretion of discount on convertible notes	1,808
Impairment of fixed assets	785	294	1,232
Recognition of deferred revenue	(4,583)	(5,371)	(5,219)
Deferred tax provision (benefit)	1,963	(2,932)	(360)
Other	96	546	(282)
Decrease (increase) in operating assets:
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	282,941	(61,723)	(224,357)
Loans, forgivable loans and other receivables from employees and partners, net	(70,038)	(53,989)	(91,176)
Accrued commissions receivable, net	(4,928)	(22,195)	21,314
Securities owned	(5,695)	(8,355)	(1,362)
Receivables from related parties	(2,447)	7,959	321
Cash segregated under regulatory requirements	(570)	(198)	2,901
Other assets	(10,413)	(5,050)	(9,814)
Reverse repurchase agreements with related parties			151,224
Increase (decrease) in operating liabilities:
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	(293,140)	48,214	261,475
Payables to related parties	9,405	(53,907)	12,185
Accounts payable, accrued and other liabilities	(15,438)	10,449	81,300
Accrued compensation	(82,972)	12,485	87
Securities sold, not yet purchased		(11)	(310)
Net cash provided by operating activities	85,344	58,912	374,613
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of fixed assets	(27,190)	(29,106)	(29,136)
Capitalization of software development costs	(15,940)	(14,831)	(15,472)
Investment in unconsolidated entities	(1,749)	(8,874)	(5,301)
Payments for acquisitions, net of cash acquired	(46,703)	(4,382)	(5,140)
Purchases of marketable securities		(3,002)
Capitalization of trademarks, patent defense and registration costs	(1,064)	(990)	(1,469)
Net cash used in investing activities	(92,646)	(61,185)	(56,518)
CASH FLOWS FROM FINANCING ACTIVITIES:
Collateralized borrowings, net	4,153	21,672	17,586
Repayment of Newmark debt	(13,835)
Issuance of convertible notes	155,620
Purchase of capped call	(11,392)
Earnings distributions to limited partnership interests in BGC Holdings	(84,332)	(49,733)	(42,117)
Redemption of limited partnership interests	(1,841)	(23,838)
Dividends to stockholders	(77,244)	(42,606)	(24,171)
Proceeds from offering of Class A common stock, net	15,632	15,160
Repurchase of Class A common stock	(392)	(19,871)	(7,911)
Partner purchase of founding/working partner units	63	1,263
Proceeds from exercises of stock options	8,812	463
Short-term borrowings	13,600
Long-term borrowings		(150,000)
Issuance of convertible notes to Cantor		150,000
Tax impact on exercise/delivery of equity awards	3,357
Cancellation of restricted stock units in satisfaction of withholding tax requirements	(3,580)	(2,246)	(657)
Net cash provided by (used in) financing activities	8,621	(99,736)	(57,270)
Effect of exchange rate changes on cash and cash equivalents	4,290	(3,188)	3,546
Net increase (decrease) in cash and cash equivalents	5,609	(105,197)	264,371
Cash and cash equivalents at beginning of period	364,104	469,301	204,930
Cash and cash equivalents at end of period	369,713	364,104	469,301
Supplemental cash information:
Cash paid during the period for taxes	16,682	20,873	15,877
Cash paid during the period for interest	20,520	9,363	9,920
Supplemental non-cash information
Conversion of Class B common stock into Class A common stock		6	37
Issuance of Class A common stock upon exchange of Cantor units	8,407	6,181
Issuance of Class B common stock upon exchange of Cantor units	8,407
Issuance of Class A common stock upon exchange of limited partnership interests	79,115	24,583	9,650
Issuance of contingent Class A common stock for acquisitions	26,778	3,171
Donations with respect to Charity Day	$ 12,076	$ 7,403