CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net income	$ 3,212	$ 37,165
Adjustments to reconcile Net income to net cash provided by operating activities
Depreciation and amortization	19,038	21,905
Stock and unit-based compensation	2,997	17,110
Realized gain on sale of assets and investments	(4,834)	(2,798)
Realized gain on repurchase of debt	0	(3,676)
Unrealized gain on investments	(117)	(4,847)
Other	618	2,750
(Increase) decrease in operating assets
Cash and cash equivalents segregated under federal and other regulations	(600)	0
Financial instruments owned, at fair value	219,419	(92,151)
Securities borrowed	93,780	(45,605)
Receivable from brokers, dealers and clearing organizations	31,107	25,130
Other assets	(34,821)	13,150
Increase (decrease) in operating liabilities
Financial instruments sold, not yet purchased, at fair value	(138,165)	(57,943)
Securities loaned	86,901	63,981
Financial instruments sold under agreements to repurchase	(75,191)	(45,599)
Other collateralized financing	(50,000)	0
Payable to brokers, dealers and clearing organizations	(23,648)	300,855
Payable to customers	28,735	(5,747)
Accrued compensation expense	(77,207)	(81,994)
Accrued expenses and other liabilities	276	(9,357)
Income taxes payable	(8,155)	0
Net cash provided by operating activities	73,345	132,329
Cash flows from investing activities
Cash received from sale of KCG Hotspot	6,492	6,552
Cash received from sale of assets	0	4,970
Cash received from sale of investments and redemptions from investments	7,404	6,534
Purchases of fixed assets and leasehold improvements	(21,776)	(12,677)
Capitalization of software development costs	(17,725)	(9,013)
Purchases of investments	(869)	(770)
Net cash used in investing activities	(26,474)	(4,404)
Cash flows from financing activities
Repurchase of 6.875% Senior Secured Notes	0	(30,288)
Borrowings under capital lease obligations	12,257	0
Principal payments on capital lease obligations	(568)	(507)
Cost of common stock repurchased	(28,849)	(30,667)
Stock options exercised	2,775	0
Warrants exercised	4,144	0
Cost of warrants repurchased	0	(967)
Net cash used in financing activities	(10,241)	(62,429)
Effect of exchange rate changes on cash and cash equivalents	1,005	261
Increase in cash and cash equivalents	37,635	65,757
Cash and cash equivalents at beginning of period	632,234	581,313
Cash and cash equivalents at end of period	669,869	647,070
Supplemental disclosure of cash flow information:
Cash paid for interest	31,891	27,884
Cash paid for income taxes	1,535	9,955
Non-cash investing activities - Compensation capitalized for internal use software that will be paid in a subsequent period	186	0
Non-cash investing activities - Compensation capitalized for internal use software that will be paid in a subsequent period	1,762	0
Non-cash financing activities - Warrants repurchased via GA Swap	$ 2,929	$ 0