The percentage of increase in cash dividend rate during the period.

No definition available.

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Namespace Prefix:	gcbc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the declared dividend will be paid, in YYYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-3

+ Details

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

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The per share amount of a dividend declared, but not paid, as of the financial reporting date.

+ References

+ Details

Name:	us-gaap_DividendsPayableAmountPerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the dividend to be paid was declared, in YYYY-MM-DD format.

+ References

+ Details

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

- Definition

Date the holder must own the stock to be entitled to the dividend, in YYYY-MM-DD format.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DividendsAxis=gcbc_O2024Q4DividendsMember
Namespace Prefix:
Data Type:	na
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Period Type:

Dividends (Details) - $ / shares		3 Months Ended	12 Months Ended
Dividends (Details) - $ / shares	Jul. 17, 2024	Sep. 30, 2024	Jun. 30, 2024
Dividends [Abstract]
Dividends payable, amount per share (in dollars per share)	$ 0.36
Common stock, dividends declared (in dollars per share)			$ 0.32
Percentage of increase in cash dividend rate	12.50%
Q4-2024 Quarterly Dividend [Member]
Dividends [Abstract]
Dividends payable, date declared		Jul. 17, 2024
Common stock, dividends declared (in dollars per share)		$ 0.09
Dividends payable, date of record		Aug. 15, 2024
Dividends payable, date paid		Aug. 30, 2024