Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Significant Accounting Policies [Line Items]
Client reimbursements	$ 1,300,000	$ 1,600,000	$ 4,800,000	$ 5,400,000
Cash on deposit with financial institutions	30,344,000	38,107,000	30,344,000	38,107,000	50,324,000	62,050,000
Carrying value of cash equivalents	6,800,000		6,800,000		4,500,000
Cash and cash equivalents, restricted from use	5,200,000		5,200,000		7,100,000
Bad debt expense	0	0	0	0
Long term receivables related to private equity and real estate capital advisory engagements	24,900,000		24,900,000		28,100,000
Installments period			3 years	3 years
Decrease in goodwill due to foreign currency translation			15,800,000
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
Deferred Compensation Plan
Significant Accounting Policies [Line Items]
Cash and cash equivalents, restricted from use	900,000		900,000		2,600,000
Capital advisory engagements
Significant Accounting Policies [Line Items]
Interest income on long term receivables	$ 300,000	$ 500,000	$ 600,000	$ 900,000
Minimum [Member] | Restricted Stock [Member]
Significant Accounting Policies [Line Items]
Compensation expense amortization period/service period following the date of grant			3 years
Maximum [Member] | Restricted Stock [Member]
Significant Accounting Policies [Line Items]
Compensation expense amortization period/service period following the date of grant			5 years