Acquisitions - Schedule of Calculation of Purchase Consideration Transferred (Parenthetical) (Detail) - GFI Group Inc. [Member]	Feb. 26, 2015 $ / shares shares
Business Acquisition [Line Items]
Cost value of shares already owned, shares	17,075,464
Number of shares under redeemable noncontrolling interest	56,435,876
Price per share of redeemable noncontrolling interest | $ / shares	$ 6.10
Appreciation of shares already owned, shares	17,075,464
Appreciation of shares already owned, per share | $ / shares	$ 6.10