Acquisitions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		12 Months Ended
	Jan. 12, 2016	Apr. 28, 2015	Feb. 26, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Business Acquisition [Line Items]
Number of shares owned prior to Acquisition			17,100,000
Stock issued during period, value, new issues				$ 175		$ 1,108
Additional goodwill recognized				814,105		$ 811,766
Total revenues				639,036	$ 547,567
Aggregate professional fees				15,410	23,281
Gain on Acquisition				$ 9,499	$ 29,040
Class A Common Stock [Member]
Business Acquisition [Line Items]
Common stock, par value				$ 0.01		$ 0.01
Stock issued during period, shares, new issues				27,226		129,151
Stock issued during period, value, new issues						$ 1
GFI Group Inc. [Member]
Business Acquisition [Line Items]
Business acquisition date				Feb. 26, 2015
Common stock, par value			$ 6.10
Tendered shares purchased			54,300,000
Percentage of outstanding common stock owned by parent	100.00%	67.00%	56.00%	100.00%
Payment date for tendered shares				Mar. 04, 2015
Payment for tendered shares aggregate amount			$ 331,100
Number of shares owned prior to Acquisition					17,100,000
Stock issued during period, shares, new issues		43,000,000
Closing price per share		$ 5.81
Stock issued during period, value, new issues		$ 250,000
Senior Notes maturity date				Jun. 19, 2018
Debt instrument, description of reference rate				LIBOR
Debt instrument, basis point		2.00%
Cash paid in connection with closing of Back-End Mergers	$ 111,200		331,100
Additional goodwill recognized			$ 450,000
Total revenues				$ 154,300	$ 64,400
Breakage costs					24,700
Severance and compensation restructuring charges					22,200
Aggregate professional fees					24,900
Gain on Acquisition					$ 29,000
GFI Group Inc. [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Common stock, par value			$ 0.01
GFI Group Inc. [Member] | Class A Common Stock [Member]
Business Acquisition [Line Items]
Business acquisition, equity interest issued, number of shares	23,500,000
Financial Services [Member]
Business Acquisition [Line Items]
Additional goodwill recognized			$ 450,000	415,709		418,929
Real Estate Services [Member]
Business Acquisition [Line Items]
Additional goodwill recognized				398,396		$ 392,837
Total consideration transferred				3,600
Business acquisition, contingent cash consideration				$ 1,400