Stock Transactions and Unit Redemptions - Summary of Changes in Carrying Amount of Redeemable Partnership Interest (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Unit Redemptions And Stock Transactions [Abstract]
Balance at beginning of period	$ 78,839	$ 86,269	$ 86,269
Consolidated net income allocated to founding/working partner units	5,631	2,367
Earnings distributions	(1,181)
Re-allocation of equity due to additional investment by founding/working partners	938	144
Founding/working partner units exchanged	(1,541)	(1,716)
Founding/working partner units redeemed	(2,583)	(3,895)
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units		(2,732)	(2,732)
Other	(729)	(2)
Balance at end of period	$ 79,374	$ 80,435	$ 78,839

- Definition

The aggregate amount to be paid by the entity upon redemption of the security that is classified as temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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