Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Additional Information (Detail)

v2.4.1.9
Commitments and Contingencies - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Commitments And Contingencies [Line Items]        
Operating lease rent expense $ 3,667us-gaap_LeaseAndRentalExpense $ 3,558us-gaap_LeaseAndRentalExpense $ 3,588us-gaap_LeaseAndRentalExpense  
Sub-lease income 379us-gaap_OperatingLeasesRentExpenseSubleaseRentals1 805us-gaap_OperatingLeasesRentExpenseSubleaseRentals1 764us-gaap_OperatingLeasesRentExpenseSubleaseRentals1  
Assets acquired under capital leases 321us-gaap_CapitalLeaseObligationsIncurred      
Depreciation expense   546us-gaap_Depreciation 423us-gaap_Depreciation 471us-gaap_Depreciation
Contingent consideration payments 1,805us-gaap_PaymentsToAcquireBusinessesGross 703us-gaap_PaymentsToAcquireBusinessesGross 720us-gaap_PaymentsToAcquireBusinessesGross  
Payments recorded as compensation expense 0samg_CompensationExpense 31samg_CompensationExpense    
MCG Acquisition | Contingent Consideration        
Commitments And Contingencies [Line Items]        
Contingent consideration percentage of EBITDA 22.00%samg_ContingentConsiderationPercentage
/ us-gaap_BusinessAcquisitionAxis
= samg_McgAcquisitionMember
/ us-gaap_ContingentConsiderationByTypeAxis
= samg_BusinessAcquisitionContingentConsiderationMember
     
Number of years contingent consideration adjusted annual EBITDA 5 years      
Contingent consideration payments 1,805us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= samg_McgAcquisitionMember
/ us-gaap_ContingentConsiderationByTypeAxis
= samg_BusinessAcquisitionContingentConsiderationMember
703us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= samg_McgAcquisitionMember
/ us-gaap_ContingentConsiderationByTypeAxis
= samg_BusinessAcquisitionContingentConsiderationMember
720us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= samg_McgAcquisitionMember
/ us-gaap_ContingentConsiderationByTypeAxis
= samg_BusinessAcquisitionContingentConsiderationMember
 
Capital Lease Assets        
Commitments And Contingencies [Line Items]        
Depreciation expense 81us-gaap_Depreciation
/ us-gaap_LeaseArrangementTypeAxis
= samg_CapitalLeaseAssetsMember
19us-gaap_Depreciation
/ us-gaap_LeaseArrangementTypeAxis
= samg_CapitalLeaseAssetsMember
19us-gaap_Depreciation
/ us-gaap_LeaseArrangementTypeAxis
= samg_CapitalLeaseAssetsMember
 
Additional Office Space        
Commitments And Contingencies [Line Items]        
Operating lease rent expense, net 5us-gaap_OperatingLeasesRentExpenseNet
/ us-gaap_MajorPropertyClassAxis
= samg_AdditionalOfficeSpaceMember
     
Refundable security deposit 3us-gaap_SecurityDeposit
/ us-gaap_MajorPropertyClassAxis
= samg_AdditionalOfficeSpaceMember
     
Lease expires Jul. 31, 2019      
Number of rent free periods 3 months      
Office Equipment        
Commitments And Contingencies [Line Items]        
Lease expires Nov. 30, 2018      
Capital lease obligation 282us-gaap_CapitalLeaseObligations
/ us-gaap_MajorPropertyClassAxis
= us-gaap_OfficeEquipmentMember
19us-gaap_CapitalLeaseObligations
/ us-gaap_MajorPropertyClassAxis
= us-gaap_OfficeEquipmentMember
   
Assets acquired under capital leases 321us-gaap_CapitalLeaseObligationsIncurred
/ us-gaap_MajorPropertyClassAxis
= us-gaap_OfficeEquipmentMember
     
Capital lease, period 5 years      
Capital lease, minimum monthly payment 5samg_CapitalLeasesMonthlyMinimumPayments
/ us-gaap_MajorPropertyClassAxis
= us-gaap_OfficeEquipmentMember
     
Letter of Credit        
Commitments And Contingencies [Line Items]        
Refundable security deposit 586us-gaap_SecurityDeposit
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember
     
Boston landlord | Letter of Credit        
Commitments And Contingencies [Line Items]        
Refundable security deposit 80us-gaap_SecurityDeposit
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember
/ dei_LegalEntityAxis
= samg_BostonLandlordMember
     
General, Administrative and Other Expenses        
Commitments And Contingencies [Line Items]        
Operating lease rent expense, net $ 3,288us-gaap_OperatingLeasesRentExpenseNet
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
$ 2,753us-gaap_OperatingLeasesRentExpenseNet
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
$ 2,824us-gaap_OperatingLeasesRentExpenseNet
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember