Acquisitions - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended		1 Months Ended		1 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Mar. 31, 2011	Sep. 30, 2012 Corporate Finance Segment	Mar. 31, 2012 Corporate Finance Segment	Mar. 31, 2011 Customer Relationships
Business Acquisition [Line Items]
Aggregate cash consideration			$ 27.1	$ 1.2	$ 2.0
Contingent consideration estimated fair value				25.0	1.1
Contingent consideration payment, due date				Dec. 31, 2017
Contingent consideration cap amount				16
Initial acquisition price					3.1
Purchase price allocation, identifiable intangible assets					0.9
Purchase price allocation, goodwill			14.8		2.2
Acquisition-date fair value of the total consideration transferred			30.0
Contingent consideration estimated fair value			2.9
Purchase price allocation, accounts receivable			24.2
Purchase price allocation, assumed liabilities			20.6
Purchase price allocation, identifiable intangible assets			6.3
Acquisition-related costs		1.5
Weighted average amortization period (in years)						12 years 4 months 24 days
Common stock consideration in relation to price protection provision guarantees	$ 3.6
Stock floor prices for common stock price guarantee provisions, minimum	$ 54.33
Stock floor prices for common stock price guarantee provisions, maximum	$ 69.48
Determination dates for common stock price guarantee provisions	2013