CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income	$ 249,104	$ 61,102	$ 126,172
(Loss) income from discontinued operations, net of tax	0	(1,332)	80
Income from continuing operations, net of tax	249,104	62,434	126,092
Adjustments to reconcile income from continuing operations, net of tax to net cash provided by operating activities
Realized gain on investments	(19,751)	0	0
Unrealized gain on investments	(10,173)	(36,456)	(4,539)
Stock and unit-based compensation	84,663	58,940	64,286
Depreciation and amortization	90,231	81,448	55,570
Non-cash gain on Knight Common Stock	0	0	(127,972)
Deferred taxes	9,976	19,397	(103,499)
Debt discount accretion and other debt related expenses	12,829	13,217	17,332
Writedown of assets and other real estate related charges	56,642	8,625	14,748
Deferred rent	2,075	930	58
Change in value in receivable from BATS	(2,102)	0	0
Realized gain from reclassification of available for sale securities	(497)	0	0
Operating activities from discontinued operations	0	(1,073)	6,952
Decrease (increase)in operating assets
Cash and cash equivalents segregated under federal and other regulations	361	(54,955)	19,963
Financial instruments owned, at fair value	265,763	14,468	(129,035)
Securities borrowed	(4,223)	(274,675)	(146,145)
Receivable from brokers, dealers and clearing organizations	507,623	(321,087)	252,266
Other assets	(26,340)	(6,459)	25,785
(Decrease) increase in operating liabilities
Financial instruments sold, not yet purchased, at fair value	(172,302)	120,207	139,951
Securities loaned	(244,368)	(25,486)	106,339
Financial instruments sold under agreements to repurchase	21,327	292,625	95,950
Payable to brokers, dealers and clearing organizations	(402,285)	268,563	(185,992)
Payable to customers	(4,724)	92,096	(46,877)
Accrued compensation expense	21,726	(29,536)	24,441
Accrued expenses and other liabilities	(37,545)	(40,583)	(64,470)
Net cash provided by operating activities	12,984	242,524	141,204
Cash flows from investing activities
Proceeds and distributions from investments	34,620	58,660	3,251
Purchases of fixed assets and leasehold improvements	(34,581)	(34,139)	(25,147)
Capitalized software development costs	(24,530)	(14,859)	(2,556)
Purchases of investments	(7,959)	(744)	(158)
Investing activities from discontinued operations	0	0	12,963
Sale of trading rights	0	554	0
Net cash provided by investing activities	328,478	11,472	582,892
Cash flows from financing activities
Proceeds from issuance of 6.875% Senior Secured Notes, net	494,810	0	0
Repayment of 8.25% Senior Secured Notes	(305,000)	0	0
Repayment of convertible notes	(117,259)	0	0
Issuance of equity to General Atlantic	0	0	55,000
Payment to former Knight Capital Group, Inc. stockholders	0	0	(720,000)
Payment of debt issuance costs	(12,645)	0	(34,592)
Borrowings under capital lease obligations	0	5,892	0
Principal payments on capital lease obligations	(4,033)	(9,232)	(14,152)
Cost of common stock repurchased - Tender Offer	(330,000)	0	0
Cost of common stock repurchased	(63,194)	(111,585)	(11,324)
Stock options exercised	1,247	0	0
Warrants exercised	532	0	0
Cost of warrants repurchased	(4,441)	0	0
Income tax provision on stock awards exercised	2,647	0	0
Proceeds from issuance of Credit Agreement	0	0	535,000
Partial repayment of Credit Agreement	0	(235,000)	(300,000)
Proceeds from issuance of Senior Secured Notes	0	0	305,000
Repayment of Knight Convertible Notes	0	0	(257,741)
Funding of collateral account for Knight Convertible Notes	0	0	(117,259)
Release of collateral account for Knight Convertible Notes	0	0	117,259
Borrowings under secured credit facility	0	0	25,000
Repayment of secured credit facility	0	0	(25,000)
Members' distributions	0	0	(21,002)
Repayment of Notes	0	0	(15,000)
Net cash used in financing activities	(337,336)	(349,925)	(478,811)
Effect of exchange rate changes on cash and cash equivalents	(1,581)	416	1,365
Increase (decrease) in cash and cash equivalents	2,545	(95,513)	246,650
Cash and cash equivalents at beginning of period	578,768	674,281	427,631
Cash and cash equivalents at end of period	581,313	578,768	674,281
Supplemental disclosure of cash flow information:
Cash paid for interest	81,349	76,003	56,227
Cash paid for income taxes	124,461	16,975	10,198
Non-cash investing activities - Contribution of fixed assets to joint venture	3,370	0	0
Knight Capital Group
Adjustments to reconcile income from continuing operations, net of tax to net cash provided by operating activities
Non-cash gain on Knight Common Stock			(128,000)
Cash flows from investing activities
Cash acquired upon acquisition of Knight Capital Group, Inc.	0	0	509,133
KCG Hotspot
Adjustments to reconcile income from continuing operations, net of tax to net cash provided by operating activities
Gain on sale of businesses	(385,026)	0	0
Cash flows from investing activities
Cash received from sale of KCG Hotspot, net of cash provided	360,928	0	0
Future Commission Merchant [Member]
Adjustments to reconcile income from continuing operations, net of tax to net cash provided by operating activities
Gain on sale of businesses	0	(116)	0
Cash flows from investing activities
Cash received from sale of Urban Financial of America, LLC	0	2,000	0
Urban Financial Group, Inc. [Member]
Cash flows from investing activities
Cash received from sale of Urban Financial of America, LLC	$ 0	$ 0	$ 85,406