| COMMITMENTS AND CONTINGENCIES (Summary of Commitments And Contingent Liabilities) (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | 
|---|---|---|---|
| Commitments to extend credit | $ 1,156,682sfbs_CommitmentsToExtendCredit | $ 1,052,902sfbs_CommitmentsToExtendCredit | $ 824,047sfbs_CommitmentsToExtendCredit | 
| Credit card arrangements | 45,155sfbs_CreditCardArrangements | 38,122sfbs_CreditCardArrangements | 25,699sfbs_CreditCardArrangements | 
| Standby letters of credit and financial guarantees | 33,280sfbs_StandbyLettersOfCreditAndFinancialGuarantees | 40,371sfbs_StandbyLettersOfCreditAndFinancialGuarantees | 36,374sfbs_StandbyLettersOfCreditAndFinancialGuarantees | 
| Total | $ 1,235,117us-gaap_OtherCommitment | $ 1,131,395us-gaap_OtherCommitment | $ 886,120us-gaap_OtherCommitment | 
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- Definition The minimum amount the entity agreed to spend under commitment to extend credit. No definition available. 
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- Definition The minimum amount the entity agreed to spend under commitment to credit card arrangement. No definition available. 
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- Definition The minimum amount the entity committed to spend for standby letters of credit and financial guarantees. No definition available. 
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- Definition Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions. No definition available. 
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