Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 01, 2018 USD ($)
Significant Accounting Policies [Line Items]
Client reimbursements	$ 4,700	$ 6,500	$ 5,400
Bad debt expense	1,100	400	300
Long term receivables related to primary capital advisory engagements	$ 29,300	26,100
Installments period	3 years
Interest income related to capital advisory engagements	$ 700	800	900
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
Total assets	$ 610,817	456,682	$ 423,144
Liabilities	$ 402,515	$ 165,499
Revenue
Significant Accounting Policies [Line Items]
Percentage of revenues earned from interest income and investment gains (losses) on investments (less than)	1.00%
Aircraft
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (or lesser for Leaseholds)	7 years
Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (or lesser for Leaseholds)	5 years
Furniture and fixtures
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (or lesser for Leaseholds)	7 years
Leasehold improvements
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (or lesser for Leaseholds)	10 years
Estimated useful lives of fixed assets, description	Lesser of 10 years or the remaining lease term
Minimum
Significant Accounting Policies [Line Items]
Amortization period of deferred cash retention awards	3 years
Minimum | Restricted Stock
Significant Accounting Policies [Line Items]
Amortization period of restricted stock units	4 years
Maximum
Significant Accounting Policies [Line Items]
Amortization period of deferred cash retention awards	5 years
Maximum | Restricted Stock
Significant Accounting Policies [Line Items]
Amortization period of restricted stock units	5 years
Accounting Standards Update 2014-09 | Forecast
Significant Accounting Policies [Line Items]
Total assets				$ 2,600
Liabilities				10,200
Decrease in equity				$ 7,600