Name:	subk_FederalHomeLoanBankBorrowings
Namespace Prefix:	subk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

Name:	us-gaap_AdvancesFromFederalHomeLoanBanks
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The calculated average balance outstanding for the year for all Federal Home Loan Bank advances as of the Balance Sheet date.

Name:	us-gaap_FederalHomeLoanBankAdvancesActivityForYearAverageBalanceOfAgreementsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The calculated weighted average interest rate for Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

Name:	us-gaap_FederalHomeLoanBankAdvancesActivityForYearAverageInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The maximum balance outstanding at any month end during the period as of the Balance Sheet date.

Name:	us-gaap_FederalHomeLoanBankAdvancesActivityForYearMaximumOutstandingAtAnyMonthEnd
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

States the weighted average interest rate applicable to the advances from the Federal Home Loan Bank outstanding as of the Balance Sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(3)(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 3

-Section VII

-Subsection 1

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Aggregate amount of interest expense on all borrowings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.7,8)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882