Loans transferred into other real estate owned.

No definition available.

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Balance Type:	debit
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- Definition

Number of real estate properties write down.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
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- Definition

number of real estate property sold.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Real estate write down during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Write down of real estate specific properties.

+ References

No definition available.

+ Details

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Namespace Prefix:	snbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net gain (loss) resulting from sales and other disposals of real estate owned for investment purposes.

+ References

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 210.9-04.14(d))

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 14

-Subparagraph d

-Article 9

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash inflow from proceeds From Sales of Wholly Owned Real Estate and Real Estate Acquired in Settlement of Loans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

+ Details

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

- Definition

Amount of other deductions to real estate investments, excluding sales, for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28.4)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

+ Details

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Balance Type:	credit
Period Type:	duration

- Details

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- Details

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- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_ResidentialRealEstateMember
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Real Estate Owned - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Property	Dec. 31, 2013	Dec. 31, 2012
Real Estate Properties [Line Items]
Loans transferred into other real estate owned	$ 945
Loans into real estate owned	1,554	7,503	3,559
Write-down of real estate owned	831snbc_RealEstateWriteDownDuringPeriod
Net loss on sales of real estate	469	1,209	345
Number of units in real estate property maintained	3
Bank Properties [Member]
Real Estate Properties [Line Items]
Real estate owned portfolio includes properties	1
Loans into real estate owned	378
Residential Properties [Member]
Real Estate Properties [Line Items]
Real estate owned portfolio includes properties	4
Loans into real estate owned	567
Write-down of real estate owned	67
Number of real estate write down	1
Number of real estate property sold	15
Write down of real estate specific properties	1,700
Commercial Properties [Member]
Real Estate Properties [Line Items]
Write-down of real estate owned	764
Number of real estate write down	2
Number of real estate property sold	1
Write down of real estate specific properties	$ 373