Investments in Securities - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Securities classified as held to maturity	$ 0.0	$ 0.0
Fair Value of Debt Securities Reported Less Than Their Historical Cost	$ 24.2	$ 116.2
Debt Securities Reported Less Than Their Historical Cost Percent of Investment Portfolio	5.80%	31.10%
Fixed rates of interest
Marketable Securities [Line Items]
Agency collateralized mortgage obligations	$ 156.8
Mortgage Backed Securities	169.9
Variable rates of interest
Marketable Securities [Line Items]
Agency collateralized mortgage obligations	19.8
Federal National Mortgage Association Certificates and Obligations (FNMA)
Marketable Securities [Line Items]
Agency collateralized mortgage obligations	52.9
Agency mortgage-backed securities	156.6
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Marketable Securities [Line Items]
Agency collateralized mortgage obligations	17.9
Agency mortgage-backed securities	10.3
Government National Mortgage Association Certificates and Obligations (GNMA)
Marketable Securities [Line Items]
Agency collateralized mortgage obligations	105.8
Agency mortgage-backed securities	$ 3.0

Represents the monetary amount of Agency collateralized mortgage obligations, as of the indicated date.

No definition available.

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- Definition

Represents the monetary amount of Agency mortgage-backed securities, as of the indicated date.

+ References

No definition available.

+ Details

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- Definition

Represents the Debt Securities Reported Less Than Their Historical Cost Percent of Investment Portfolio, as of the indicated date.

+ References

No definition available.

+ Details

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- Definition

Represents the monetary amount of Fair Value of Debt Securities Reported Less Than Their Historical Cost, as of the indicated date.

+ References

No definition available.

+ Details

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- Definition

Represents the monetary amount of Mortgage-backed securities, as of the indicated date.

+ References

No definition available.

+ Details

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Namespace Prefix:	gsbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: 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=121553693&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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- Definition

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.

+ References

No definition available.

+ Details

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