Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) Segment	Mar. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Contract with customer, liability	$ 16,800,000		$ 12,300,000
Client reimbursements	1,200,000	$ 1,000,000
Unfunded commitment	$ 0			$ 0
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.
Retained earnings	$ (34,631,000)			(37,595,000)
Reimbursable expense	$ 1,200,000
Number of business segments | Segment	1
Minimum
Significant Accounting Policies [Line Items]
Amortization period of deferred cash retention awards	3 years
Maximum
Significant Accounting Policies [Line Items]
Amortization period of deferred cash retention awards	5 years
Revenue | Maximum
Significant Accounting Policies [Line Items]
Percent of revenues	1.00%
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, maximum (in years)	Lesser of 10 years or the remaining lease term
Restricted Stock | Minimum
Significant Accounting Policies [Line Items]
Restricted stock units, amortization service period (years)	4 years
Restricted Stock | Maximum
Significant Accounting Policies [Line Items]
Restricted stock units, amortization service period (years)	5 years
Capital advisory engagements
Significant Accounting Policies [Line Items]
Interest income	$ 200,000	$ 200,000
ASC 606 Adjustments | Accounting Standards Update 2014-09
Significant Accounting Policies [Line Items]
Retained earnings			7,600,000
Deferred revenue			10,200,000
Deferred income tax assets, net			$ 2,600,000
Primary Capital Advisory Engagements
Significant Accounting Policies [Line Items]
Long term receivables related to private equity and real estate capital advisory engagements	$ 27,600,000			$ 29,300,000
Installments period (in years)	3 years