Investments - Equity Method Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Equity method investments	$ 17,703	$ 25,556
ELX [Member]
Investment [Line Items]
Percent Ownership	49.00%
Equity method investments	6,469	14,337
Freedom International Brokerage [Member]
Investment [Line Items]
Percent Ownership	45.00%
Equity method investments	8,370	8,976
China Credit BGC Money Broking Company Limited [Member]
Investment [Line Items]
Percent Ownership	33.00%
Equity method investments	2,004	1,485
Aqua and Other Investments [Member]
Investment [Line Items]
Equity method investments	$ 860	$ 758