LOANS, Non-accrual Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	$ 12,981	$ 15,183
Percentage of Total (in hundredths)	100.00%	100.00%
Total Loans	1,355,427	1,068,848
Percentage of Total Loans (in hundredths)	1.00%	1.40%
Additional interest income for the non-accrual loans outstanding at the end of the reported periods	953	521	854
Commercial and Industrial [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	4,060	5,014
Percentage of Total (in hundredths)	31.30%	33.00%
Total Loans	177,813	171,199
Percentage of Total Loans (in hundredths)	0.30%	0.40%
Commercial Real Estate [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	6,556	7,492
Percentage of Total (in hundredths)	50.50%	49.30%
Total Loans	560,524	464,560
Percentage of Total Loans (in hundredths)	0.50%	0.70%
Multifamily [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	0	0
Percentage of Total (in hundredths)	0.00%	0.00%
Total Loans	309,666	184,624
Percentage of Total Loans (in hundredths)	0.00%	0.00%
Mixed Use Commercial [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	0	0
Percentage of Total (in hundredths)	0.00%	0.00%
Total Loans	34,806	4,797
Percentage of Total Loans (in hundredths)	0.00%	0.00%
Real Estate Construction [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	0	0
Percentage of Total (in hundredths)	0.00%	0.00%
Total Loans	26,206	6,565
Percentage of Total Loans (in hundredths)	0.00%	0.00%
Residential Mortgages [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	2,020	1,897
Percentage of Total (in hundredths)	15.60%	12.50%
Total Loans	187,828	169,552
Percentage of Total Loans (in hundredths)	0.10%	0.20%
Home Equity [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	303	647
Percentage of Total (in hundredths)	2.30%	4.30%
Total Loans	50,982	57,112
Percentage of Total Loans (in hundredths)	0.10%	0.10%
Consumer [Member]
Summarizes non-accrual loans by loan class
Non-accrual Loans principal balance	42	133
Percentage of Total (in hundredths)	0.30%	0.90%
Total Loans	$ 7,602	$ 10,439
Percentage of Total Loans (in hundredths)	0.00%	0.00%

Financing receivable recorded investment non accrual status percentage.

No definition available.

Name:	subk_FinancingReceivableRecordedInvestmentNonAccrualStatusPercentage
Namespace Prefix:	subk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans and leases receivable ratio of nonaccrual loans to all loans.

+ References

No definition available.

+ Details

Name:	subk_LoansAndLeasesReceivableRatioOfNonaccrualLoansToAllLoans
Namespace Prefix:	subk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	subk_SummarizesNonAccrualLoansByLoanClassAbstract
Namespace Prefix:	subk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

+ Details

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

- Definition

The gross interest income that would have been recorded in the period on troubled debt restructurings, if the loans had been current in accordance with their original terms and had been outstanding throughout the period or since origination, if held for part of the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=subk_MixedUseCommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=subk_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=subk_RealEstateConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: