Annual Dividend Rate Per Share

No definition available.

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Namespace Prefix:	gcbc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Details

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Period Type:	duration

- Definition

Refers to waiver of dividend by parent company to be declared by the entity.

+ References

No definition available.

+ Details

Name:	gcbc_DividendWaiverByParent
Namespace Prefix:	gcbc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-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

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

+ Details

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

- Definition

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

+ References

+ Details

Name:	us-gaap_DividendsPayableDateDeclaredDayMonthAndYear
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 CCYY-MM-DD format.

+ References

No definition available.

+ Details

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

- Details

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DividendsAxis=gcbc_DividendDeclared2014Q2Member
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_DividendsAxis=gcbc_DividendDeclared2015AnnualMember
Namespace Prefix:
Data Type:	na
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Dividends (Details) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended	12 Months Ended
Dividends (Details) (USD $)	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Jan. 20, 2015	Dec. 31, 2015
Dividends [Line Items]
Common stock, dividends, per share, declared (in dollars per share)	$ 0.180	$ 0.175	$ 0.540	$ 0.525
Dividend Declared 2014 Q2 [Member]
Dividends [Line Items]
Dividends payable, date declared			Jan. 20, 2015
Common stock, dividends, per share, declared (in dollars per share)					$ 0.18
Dividends payable, date of record			Feb. 13, 2015
Dividends payable, date to be paid			Feb. 27, 2015
Dividend Declared 2014 Annual [Member]
Dividends [Line Items]
Annual dividend rate per share (in dollars per share)			$ 0.72
Dividend Declared 2015 Annual [Member] \| Subsequent Event [Member]
Dividends [Line Items]
Annual dividend rate per share (in dollars per share)			$ 0.72
Mutual Holding Company [Member] \| Dividend Declared 2015 Annual [Member] \| Maximum [Member] \| Subsequent Event [Member]
Dividends [Line Items]
Dividend waiver by parent (in dollars per share)						$ 0.80