Limited Partnership Interests in BGC Holdings - Additional Information (Detail)	3 Months Ended			9 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2014 PartnershipUnit	Dec. 31, 2014 Scenario, Forecast [Member]	Dec. 31, 2014 Scenario, Forecast [Member]
Noncontrolling Interest [Abstract]
Number of operating partnerships				2
Payout period for post-termination awards				4 equal yearly installments
Percentage to preferred units	0.6875%	0.6875%	0.6875%		0.6875%	2.75%
Limited partnership interests Exchange ratio, subject to adjustment				1