Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v2.4.1.9
Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Unit
Segment
Dec. 31, 2013
Unit
Dec. 31, 2012
Jun. 26, 2013
Summary Of Significant Accounting Policies [Line Items]        
Number of operating segment 1us-gaap_NumberOfOperatingSegments      
Cash equivalents, maximum maturity period 90 days      
Equity method investments, unrealized intercompany profit (loss) not eliminated amount $ 0us-gaap_EquityMethodInvestmentUnrealizedIntercompanyProfitLossNotEliminatedAmount      
Number of reporting unit 1us-gaap_NumberOfReportableSegments 1us-gaap_NumberOfReportableSegments    
Impairment charges on goodwill 0us-gaap_GoodwillImpairmentLoss 0us-gaap_GoodwillImpairmentLoss 0us-gaap_GoodwillImpairmentLoss  
Professional and other cost related to IPO     2,816samg_ProfessionalAndOtherCost  
Minimum        
Summary Of Significant Accounting Policies [Line Items]        
Identifiable finite-lived intangible assets, useful life 3 years      
Maximum        
Summary Of Significant Accounting Policies [Line Items]        
Identifiable finite-lived intangible assets, useful life 20 years      
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 $ 0us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquityMethodInvestmentsMember 		$ 0us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquityMethodInvestmentsMember 		$ 0us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_EquityMethodInvestmentsMember 		 
Class A Common Stock        
Summary Of Significant Accounting Policies [Line Items]        
Ownership percentage in a subsidiary 63.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember 		63.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember 		  63.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
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      
Class B Common Stock | SLP        
Summary Of Significant Accounting Policies [Line Items]        
Class of share exchangeable to another class One share of Class A common stock