CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND EQUITY (USD $) In Thousands, unless otherwise specified	Total		Convertible Preferred Stock [Member]	Common Class A [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated other comprehensive loss [Member]	Knight Capital Group, Inc., Total [Member]
Balance at Dec. 31, 2012	$ 1,252,683		$ 229,857	$ 2,748	$ 1,400,317	$ 710,621	$ (858,907)	$ (2,096)	$ 1,252,683
Balance, Shares at Dec. 31, 2012			243	274,821			72,765
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(40,198)	[1]	0	0	0	(40,198)	0	0	(40,198)
Series A-1 convertible preferred stock converted into common stock			(229,857)	1,623	228,234	0	0	0	229,857
Series A-1 convertible preferred stock converted into common stock, shares			(243)	162,309			0
Knight Common Stock repurchased			0	0	(4)	0	(11,912)	0	(11,916)
Kinght common stock repurchased, Shares			0	0			(3,211)
Stock-based compensation			0	121	54,843	0	0	0	54,964
Stock-based compensation, Shares			0	12,117			0
Cumulative translation adjustment			0	0	0	0	0	(3,675)	(3,675)
Balance at Jun. 30, 2013	$ 1,481,715		$ 0	$ 4,492	$ 1,683,390	$ 670,423	$ (870,819)	$ (5,771)	$ 1,481,715
Balance, Shares at Jun. 30, 2013			0	(449,247)			(75,976)

[1] See Explanatory Note - All financial information is of Knight Capital Group, Inc. As of July 1, 2013, Knight Capital Group, Inc., became a wholly-owned subsidiary of KCG