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 $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accounting Policies [Line Items]      
Unrecognized Tax Benefits Threshold Percentage 50.00%sfbs_UnrecognizedTaxBenefitsThresholdPercentage    
Advertising Expense $ 477,000us-gaap_AdvertisingExpense $ 532,000us-gaap_AdvertisingExpense $ 454,000us-gaap_AdvertisingExpense
Federal Reserve Bank [Member]      
Accounting Policies [Line Items]      
Cash Reserve Deposit Required and Made $ 36,900,000us-gaap_CashReserveDepositRequiredAndMade
/ us-gaap_InvestmentTypeAxis
= sfbs_FederalReserveBankMember 		$ 24,400,000us-gaap_CashReserveDepositRequiredAndMade
/ us-gaap_InvestmentTypeAxis
= sfbs_FederalReserveBankMember 		 
Maximum [Member]      
Accounting Policies [Line Items]      
Property, Plant and Equipment, Useful Life 10 years    
Minimum [Member]      
Accounting Policies [Line Items]      
Property, Plant and Equipment, Useful Life 3 years