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EMPLOYEE BENEFITS (Details) (USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2012
EMPLOYEE BENEFITS [Abstract]        
Net periodic pension credit $ (111)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost $ (91)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost    
Optional required contribution for pension plan     1,000,000subk_OptionalRequiredContributionForPensionPlan  
Minimum required contribution for the pension plan     0subk_MinimumRequiredContributionForPensionPlan  
Additional minimum required contribution for the pension plan       $ 0subk_AdditionalRequiredContributionForPensionPlan