Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Client reimbursements	$ 1.5	$ 1.3	$ 3.2	$ 4.8
Long term receivables related to private equity and real estate capital advisory engagements	39.2		39.2		34.0
Installments period			3 years
Decrease to goodwill from translation adjustments			3.3
Depreciation and amortization of property and equipment			Depreciation is computed using the straight-line method over the life of the assets. Amortization of leasehold improvements is computed using the straight-line method over the lesser of the life of the asset or the remaining term of the lease.
Aircraft
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)			7 years
Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)			5 years
Furniture and Fixtures
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)			7 years
Leasehold Improvements
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)			10 years
Description of estimated useful lives			Lesser of 10 years or the remaining lease term
Capital advisory engagements
Significant Accounting Policies [Line Items]
Interest income on long term receivables	$ 0.3	$ 0.3	$ 0.7	$ 0.6