SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) Share data in Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Corporation	Dec. 31, 2013	Dec. 31, 2012
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average common shares outstanding (in shares)	11,582,807	11,570,731	10,248,751
Weighted average unvested restricted shares (in shares)	43,547	0	0
Weighted average shares for basic earnings per share (in shares)	11,626,354	11,570,731	10,248,751
Additional diluted shares: [Abstract]
Stock options	55,788	20,390	0
Weighted average shares for diluted earnings per share (in shares)	11,682,142	11,591,121	10,248,751
Organization and Nature of Operations [Abstract]
Ownership percentage (in hundredths)	100.00%
Number of corporation used to acquire foreclosed real estate	2
Loans and Loan Interest Income Recognition [Abstract]
Maximum period for accrued interest for all class of loans	90 days
Allowance for Loan Losses [Abstract]
Threshold for non-accrual loans to be evaluated individually for impairment	$ 250,000
Transfers of Financial Instruments [Abstract]
Servicing loan portfolio	160,000,000subk_ServicingLoanPortfolio	161,000,000subk_ServicingLoanPortfolio
Mortgage servicing rights	2,000,000subk_MortgageServicingRightsFairValue	2,000,000subk_MortgageServicingRightsFairValue
Other Real Estate [Abstract]
Other Real Estate Owned ("OREO")	0	0
PREMISES AND EQUIPMENT [Abstract]
Impairment of long lived assets	0us-gaap_AssetImpairmentCharges	0us-gaap_AssetImpairmentCharges
Goodwill [Abstract]
Fair value of the assets acquired	814,000us-gaap_FairValueOfAssetsAcquired
Impairment of goodwill	0us-gaap_GoodwillImpairmentLoss	0us-gaap_GoodwillImpairmentLoss
Allowance for Contingent Liabilities [Abstract]
Allowance for contingent liabilities	$ 290,000subk_AllowanceForContingentLiabilities	$ 255,000subk_AllowanceForContingentLiabilities

Allowance for contingent liabilities as on reporting date.

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Minimum loan evaluated individually for impairment.

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Carrying amount (balance) as of the balance sheet date of an "Mortgage Servicing Rights" representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Period of past due for no longer accrue interest.

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Carrying amount (balance) as of the balance sheet date of an loan portfolio representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The fair value of assets acquired in noncash investing or financing activities.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

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Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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Number of shares of restricted stock determined by relating the portion of time within a reporting period that restricted shares have been outstanding to the total time in that period. Restricted shares are subject to sales, contractual, regulatory or other restrictions that prevent or inhibit the holder from freely disposing of them before the restriction ends.

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