Disclosures about Fair Value of Financial Instruments - Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Assets:
Securities available-for-sale	$ 600,799	$ 560,479
Financial liabilities:
Repurchase agreements	25,711	16,359
Carrying Amount [Member]
Financial Assets:
Cash and cash equivalents	80,077	74,132
Securities available-for-sale	600,799	560,479
Loans and leases, net held for investment	1,753,846	1,724,575
Collateral dependent impaired loans	1,692	205
Financial liabilities:
Non-interest-bearing	690,950	662,527
Interest-bearing	1,477,424	1,453,813
Fed funds purchased and repurchase agreements	25,711	16,359
Short term borrowings	20,000	56,100
Subordinated debentures	34,945	34,767
Fair Value [Member]
Financial Assets:
Cash and cash equivalents	80,076	74,132
Securities available-for-sale	600,799	560,479
Loans and leases, net held for investment	1,761,461	1,707,463
Collateral dependent impaired loans	1,692	205
Financial liabilities:
Non-interest-bearing	690,950	662,527
Interest-bearing	1,477,497	1,453,048
Fed funds purchased and repurchase agreements	25,711	16,359
Short term borrowings	20,000	56,100
Subordinated debentures	30,564	30,311
Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	80,076	74,132
Securities available-for-sale	0	0
Loans and leases, net held for investment	0	0
Collateral dependent impaired loans	0	0
Financial liabilities:
Non-interest-bearing	690,950	662,527
Interest-bearing	0	0
Fed funds purchased and repurchase agreements	0	0
Short term borrowings	0	0
Subordinated debentures	0	0
Fair Value [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Securities available-for-sale	600,799	560,479
Loans and leases, net held for investment	0	0
Collateral dependent impaired loans	1,692	205
Financial liabilities:
Non-interest-bearing	0	0
Interest-bearing	1,477,497	1,453,048
Fed funds purchased and repurchase agreements	25,711	16,359
Short term borrowings	20,000	56,100
Subordinated debentures	30,564	30,311
Fair Value [Member] \| Fair Value, Inputs, Level 3 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Securities available-for-sale	0	0
Loans and leases, net held for investment	1,761,461	1,707,463
Collateral dependent impaired loans	0	0
Financial liabilities:
Non-interest-bearing	0	0
Interest-bearing	0	0
Fed funds purchased and repurchase agreements	0	0
Short term borrowings	0	0
Subordinated debentures	$ 0	$ 0

Interest bearing deposit liabilities, fair value disclosure.

No definition available.

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- Definition

Loans and leases held for investment.

+ References

No definition available.

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- Definition

Non interest bearing deposit liabilities, fair value disclosure.

+ References

No definition available.

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Namespace Prefix:	bsrr_
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Period Type:	instant

- Definition

Other long term debt, fair value disclosure.

+ References

No definition available.

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- Definition

Carrying amount of assets sold under agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

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- Definition

Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

No definition available.

+ Details

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- References

No definition available.

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

- References

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Namespace Prefix:	us-gaap_
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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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