Investments - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Investment [Line Items]
Gain (losses) on equity method investments	$ 600	$ 200
Share in gains (losses) related to equity method investments	558	$ 803
Cost method investments	1,492		$ 1,536
GFI Group Inc. [Member]
Investment [Line Items]
Share in gains (losses) related to equity method investments	1,000
Consolidated VIE, total assets	9,200
Consolidated VIE, total liabilities	1,300
Maximum exposure to economic loss	$ 5,200

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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