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

No definition available.

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Namespace Prefix:	gcbc_
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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

+ Details

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

- References

No definition available.

+ Details

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Period Type:	duration

- Definition

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

+ References

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
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- Details

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- Details

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- Details

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Dividends (Details) - $ / shares		3 Months Ended		6 Months Ended		12 Months Ended
Dividends (Details) - $ / shares	Oct. 16, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019
Dividends [Abstract]
Common stock, dividends, per share, declared (in dollars per share)		$ 0.11	$ 0.10	$ 0.22	$ 0.20
2020 Q1 Dividend [Member]
Dividends [Abstract]
Dividends payable, date declared				Oct. 16, 2019
Common stock, dividends, per share, declared (in dollars per share)	$ 0.11
Percentage of increase in cash dividend rate	10.00%
Dividends payable, date of record				Nov. 15, 2019
Dividends payable, date paid				Nov. 29, 2019
2020 Annual Dividend [Member]
Dividends [Abstract]
Common stock, dividends, per share, declared (in dollars per share)	$ 0.44
2019 Annual Dividend [Member]
Dividends [Abstract]
Common stock, dividends, per share, declared (in dollars per share)						$ 0.40