CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities
Net (loss) income	$ 230,139	$ 44,584
Loss from discontinued operations, net of tax	0	(1,320)
Income from continuing operations, net of tax	230,139	45,904
Adjustments to reconcile income from continuing operations, net of tax to net cash (used in) provided by operating activities
Realized gain from sale of KCG Hotspot	(385,026)	0
Deferred taxes	(25,781)	0
Unrealized gain on investments	(4,661)	(15,140)
Stock and unit-based compensation	56,422	32,907
Depreciation and amortization	41,341	39,926
Debt discount accretion and other debt related expenses	10,627	11,557
Other real estate related charges	6,459	2,207
Deferred rent	421	(129)
Receivable from BATS	(709)	0
Operating activities from discontinued operations	0	(1,119)
(Increase) decrease in operating assets
Cash and cash equivalents segregated under federal and other regulations	(239)	(51,267)
Financial instruments owned, at fair value	11,645	(167,968)
Securities borrowed	(239,250)	(245,080)
Receivable from brokers, dealers and clearing organizations	498,543	(331,675)
Other assets	(32,938)	(8,009)
(Decrease) increase in operating liabilities
Financial instruments sold, not yet purchased, at fair value	(247,549)	236,612
Securities loaned	33,988	91,433
Financial instruments sold under agreements to repurchase	62,091	309,160
Payable to brokers, dealers and clearing organizations	(146,341)	173,012
Payable to customers	16,172	141,323
Accrued compensation expense	(49,374)	(60,825)
Accrued expenses and other liabilities	6,965	(10,993)
Income taxes payable	64,107	0
Net cash (used in) provided by operating activities	(92,948)	191,836
Cash flows from investing activities
Cash received from sale of KCG Hotspot, net of cash provided	360,928	0
Proceeds and distributions from investments	2,517	48,627
Purchases of fixed assets and leasehold improvements	(13,238)	(14,781)
Capitalized software development costs	(9,244)	(5,615)
Purchases of investments	(2,376)	(593)
Sale of trading rights	0	554
Net cash provided by investing activities	338,587	28,192
Cash flows from financing activities
Repayment of Credit Agreement	0	(235,000)
Proceeds from issuance of 6.875% Senior Secured Notes, net	494,810	0
Repayment of 8.25% Senior Secured Notes	(305,000)	0
Repayment of convertible notes	(117,259)	0
Payment of debt issuance costs	(12,645)	0
Borrowings under capital lease obligations	0	4,525
Principal payments on capital lease obligations	(2,823)	(5,342)
Cost of common stock repurchased - Tender Offer	(330,000)	0
Cost of common stock repurchased	(10,653)	(58,119)
Stock options exercised	1,046	0
Warrants exercised	247	0
Income tax provision on stock awards exercised	218	0
Net cash used in financing activities	(282,059)	(293,936)
Effect of exchange rate changes on cash and cash equivalents	(1,056)	492
(Decrease) increase in cash and cash equivalents	(37,476)	(73,416)
Cash and cash equivalents at beginning of period	578,768	674,281
Cash and cash equivalents at end of period	541,292	600,865
Supplemental disclosure of cash flow information:
Cash paid for interest	39,140	39,129
Cash paid for income taxes	63,242	14,040
Non-cash investing activities - Contribution of fixed assets to joint venture	$ 1,927	$ 0