LOANS, Loans Modified as Troubled Debt Restructurings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Loan	Dec. 31, 2013 Loan	Dec. 31, 2012 Loan
Troubled debt restructuring at end of period
Number of loans	70	70
Outstanding recorded investment	$ 19,673	$ 16,085
Troubled debt restructured during year
Number of Loans	25	16	24
Outstanding Recorded Balance, pre-modification	8,983	6,450	8,340
Outstanding Recorded Balance, Post modification	8,983	6,450	8,340
Defaulted Troubled Debt Restructurings [Member]
Troubled debt restructured during year
Number of Loans	2	2	4
Outstanding Recorded Balance, pre-modification	1,529	700	1,932
Commercial and Industrial [Member]
Troubled debt restructuring at end of period
Number of loans	31	43
Outstanding recorded investment	3,683	6,022
Troubled debt restructured during year
Number of Loans	10	8	17
Outstanding Recorded Balance, pre-modification	1,877	2,484	6,674
Outstanding Recorded Balance, Post modification	1,877	2,484	6,674
Commercial and Industrial [Member] \| Defaulted Troubled Debt Restructurings [Member]
Troubled debt restructured during year
Number of Loans	0	0	2
Outstanding Recorded Balance, pre-modification	0	0	1,125
Commercial Real Estate [Member]
Troubled debt restructuring at end of period
Number of loans	8	7
Outstanding recorded investment	10,179	6,022
Troubled debt restructured during year
Number of Loans	2	3
Outstanding Recorded Balance, pre-modification	5,161	3,025
Outstanding Recorded Balance, Post modification	5,161	3,025
Commercial Real Estate [Member] \| Defaulted Troubled Debt Restructurings [Member]
Troubled debt restructured during year
Number of Loans	2	1	0
Outstanding Recorded Balance, pre-modification	1,529	390	0
Residential Mortgages [Member]
Troubled debt restructuring at end of period
Number of loans	19	17
Outstanding recorded investment	4,314	3,891
Troubled debt restructured during year
Number of Loans	4	4	6
Outstanding Recorded Balance, pre-modification	581	924	1,617
Outstanding Recorded Balance, Post modification	581	924	1,617
Residential Mortgages [Member] \| Defaulted Troubled Debt Restructurings [Member]
Troubled debt restructured during year
Number of Loans	0	1	2
Outstanding Recorded Balance, pre-modification	0	310	807
Home Equity [Member]
Troubled debt restructuring at end of period
Number of loans	5	0
Outstanding recorded investment	1,216	0
Troubled debt restructured during year
Number of Loans	5	0
Outstanding Recorded Balance, pre-modification	1,219	0
Outstanding Recorded Balance, Post modification	1,219	0
Consumer [Member]
Troubled debt restructuring at end of period
Number of loans	7	3
Outstanding recorded investment	281	150
Troubled debt restructured during year
Number of Loans	4	1	1
Outstanding Recorded Balance, pre-modification	145	17	49
Outstanding Recorded Balance, Post modification	$ 145	$ 17	$ 49

Number of financing receivables that have been modified by troubled debt restructurings held at period end.

No definition available.

Name:	subk_FinancingReceivableModificationsNumberOfContracts3
Namespace Prefix:	subk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

+ Details

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

- 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:

- Details

Name:	us-gaap_FinancingReceivableTroubledDebtRestructuringAxis=subk_DefaultTroubledDebtRestructuredMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: