Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Client reimbursements	$ 5.4	$ 4.5	$ 6.5
Bad debt expense	0.3	0.1	0.0
Long term receivables related to private equity and real estate capital advisory engagements	$ 32.4	$ 37.3
Installments period (years)	3 years	3 years
Interest income related to capital advisory engagements	$ 0.9	$ 0.9	$ 0.8
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
Estimated useful lives of fixed assets, description	Lesser of 10 years or the remaining lease term
Restricted Stock
Significant Accounting Policies [Line Items]
Compensation expense amortization period/service period following the date of grant (years)	5 years