Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
Segment
Unit
Mar. 31, 2017
USD ($)
Dec. 31, 2017
Dec. 31, 2016
Unit
Jun. 26, 2013
Summary Of Significant Accounting Policies [Line Items]          
Number of operating segment | Segment 1        
Cash equivalents, maximum maturity period 90 days        
Equity method investments, unrealized intercompany profit (loss) not eliminated amount $ 0        
Number of reporting unit | Unit 1     1  
Impairment charges on goodwill $ 0 $ 0      
Corporate tax rate 21.00%   35.00%    
Equity or Balanced Portfolios          
Summary Of Significant Accounting Policies [Line Items]          
Percentage of asset management fee on threshold limit 1.00%        
Asset under management, threshold limit $ 10,000,000        
Percentage of asset management fee on balance 0.60%        
Fixed Income Portfolios          
Summary Of Significant Accounting Policies [Line Items]          
Percentage of asset management fee on threshold limit 0.40%        
Asset under management, threshold limit $ 10,000,000        
Percentage of asset management fee on balance 0.30%        
Municipal Value Strategy          
Summary Of Significant Accounting Policies [Line Items]          
Percentage of income from asset management fee 0.65%        
Minimum          
Summary Of Significant Accounting Policies [Line Items]          
Identifiable finite-lived intangible assets, useful life 3 years        
Minimum | Private Funds          
Summary Of Significant Accounting Policies [Line Items]          
Prior written notice period to terminate investment management agreements 30 days        
Prior written notice period after receiving the affirmative vote, to terminate investment management agreements 60 days        
Percentage of income from asset management fee 0.25%        
Minimum | Non-discretionary Assets          
Summary Of Significant Accounting Policies [Line Items]          
Percentage of income from asset management fee 0.05%        
Maximum          
Summary Of Significant Accounting Policies [Line Items]          
Identifiable finite-lived intangible assets, useful life 20 years        
Maximum | Private Funds          
Summary Of Significant Accounting Policies [Line Items]          
Prior written notice period to terminate investment management agreements 90 days        
Prior written notice period after receiving the affirmative vote, to terminate investment management agreements 90 days        
Percentage of income from asset management fee 1.50%        
Maximum | Non-discretionary Assets          
Summary Of Significant Accounting Policies [Line Items]          
Percentage of income from asset management fee 0.01%        
Leasehold Improvements          
Summary Of Significant Accounting Policies [Line Items]          
Property, plant and equipment, useful life 10 years        
Other Fixed Assets | Minimum          
Summary Of Significant Accounting Policies [Line Items]          
Property, plant and equipment, useful life 3 years        
Other Fixed Assets | Maximum          
Summary Of Significant Accounting Policies [Line Items]          
Property, plant and equipment, useful life 7 years        
Equity Method Investments          
Summary Of Significant Accounting Policies [Line Items]          
Impairment charges related to equity method investments $ 0 $ 0      
Class A Common Stock          
Summary Of Significant Accounting Policies [Line Items]          
Common stock, voting rights 1 vote per share        
Class B Common Stock          
Summary Of Significant Accounting Policies [Line Items]          
Common stock, voting rights 1 vote per share        
Class of share exchangeable to another class One share of Class A common stock        
Silvercrest L.P | Class A Common Stock          
Summary Of Significant Accounting Policies [Line Items]          
Ownership percentage in a subsidiary 62.00%       61.80%
Common stock, voting rights 1 vote per share