Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Segment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Client reimbursements	$ 1.3	$ 1.2	$ 3.2
Bad debt expense	0.3	$ 0.2	0.4	$ 0.3
Long term receivables related to private equity and real estate capital advisory engagements	29.9		$ 29.9		$ 32.4
Installments period (in years)			3 years
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.
Number of business segments (segment) | Segment			1
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
Restricted Stock
Significant Accounting Policies [Line Items]
Restricted stock units, amortization service period (years)			5 years
Capital advisory engagements
Significant Accounting Policies [Line Items]
Interest income	$ 0.2		$ 0.4	$ 0.4
Revenue | Minimum
Significant Accounting Policies [Line Items]
Percent of revenues			0.00%
Revenue | Maximum
Significant Accounting Policies [Line Items]
Percent of revenues			1.00%