Acquisitions - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	1 Months Ended
	Mar. 31, 2013	Apr. 30, 2013 Series of Individually Immaterial Business Acquisitions Subsequent Event	Apr. 30, 2013 Corporate Finance Segment Subsequent Event	Mar. 31, 2013 Strategic Communications	Jan. 31, 2013 Forensic and Litigation Consulting
Business Acquisition [Line Items]
Common stock consideration in relation to price protection provision guarantees	$ 0.8	$ 2.8
Stock floor prices for common stock price guarantee provisions	$ 54.33
Contingent consideration estimated fair value			26.0	7.3	1.8
Contingent consideration payment, due date			Dec. 31, 2017	Dec. 31, 2017
Contingent consideration cap amount				8.0
Purchase price allocation, identifiable intangible assets	2.0
Purchase price allocation, goodwill	$ 8.8