XML 50 R38.htm IDEA: XBRL DOCUMENT
v3.22.4

Securities, Securities in Continuous Unrealized Loss Position (Details) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Dec. 31, 2022 USD ($) Security | Dec. 31, 2021 USD ($) | Dec. 31, 2022 USD ($) Security | Dec. 31, 2021 USD ($) | Jun. 30, 2022 USD ($) Security
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 140,953 |  | $ 140,953 |  | $ 288,207
More than 12 months, fair value | 110,327 |  | 110,327 |  | 12,078
Total, fair value | 251,280 |  | 251,280 |  | 300,285
Less than 12 months, unrealized losses | 3,616 |  | 3,616 |  | 21,161
More than 12 months, unrealized losses | 26,828 |  | 26,828 |  | 2,776
Total, unrealized losses | $ 30,444 |  | $ 30,444 |  | $ 23,937
Less than 12 months, number of securities | Security | 108 |  | 108 |  | 233
More than 12 months, number of securities | Security | 49 |  | 49 |  | 5
Total, number of securities | Security | 157 |  | 157 |  | 238
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 383,488 |  | $ 383,488 |  | $ 592,159
More than 12 months, fair value | 196,316 |  | 196,316 |  | 735
Total, fair value | 579,804 |  | 579,804 |  | 592,894
Less than 12 months, unrealized losses | 22,022 |  | 22,022 |  | 53,995
More than 12 months, unrealized losses | 41,719 |  | 41,719 |  | 183
Total, unrealized losses | $ 63,741 |  | $ 63,741 |  | $ 54,178
Less than 12 months, number of securities | Security | 3,537 |  | 3,537 |  | 2,477
More than 12 months, number of securities | Security | 641 |  | 641 |  | 5
Total, number of securities | Security | 4,178 |  | 4,178 |  | 2,482
Total Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 524,441 |  | $ 524,441 |  | $ 880,366
More than 12 months, fair value | 306,643 |  | 306,643 |  | 12,813
Total, fair value | 831,084 |  | 831,084 |  | 893,179
Less than 12 months, unrealized losses | 25,638 |  | 25,638 |  | 75,156
More than 12 months, unrealized losses | 68,547 |  | 68,547 |  | 2,959
Total, unrealized losses | $ 94,185 |  | $ 94,185 |  | $ 78,115
Less than 12 months, number of securities | Security | 3,645 |  | 3,645 |  | 2,710
More than 12 months, number of securities | Security | 690 |  | 690 |  | 10
Total, number of securities | Security | 4,335 |  | 4,335 |  | 2,720
Available for sale securities transferred at fair value to held to maturity | $ 0 | $ 0 | $ 0 | $ 0 |
Gross realized gains (losses) on sale of available-for-sale securities | (251) | 0 | $ (251) | 0 |
Number of sales of available-for-sale security | Security |  |  | 1 |  |
Proceeds from sale of available-for-sale securities |  | 0 | $ 1,675 | 0 |
Other-than-temporary impairment losses | 0 | $ 0 | 0 | $ 0 |
U.S. Government Sponsored Enterprises [Member] |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | 0 |  | 0 |  | $ 11,319
More than 12 months, fair value | 10,729 |  | 10,729 |  | 0
Total, fair value | 10,729 |  | 10,729 |  | 11,319
Less than 12 months, unrealized losses | 0 |  | 0 |  | 1,747
More than 12 months, unrealized losses | 2,332 |  | 2,332 |  | 0
Total, unrealized losses | $ 2,332 |  | $ 2,332 |  | $ 1,747
Less than 12 months, number of securities | Security | 0 |  | 0 |  | 5
More than 12 months, number of securities | Security | 5 |  | 5 |  | 0
Total, number of securities | Security | 5 |  | 5 |  | 5
U.S. Treasury Securities [Member] |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 535 |  | $ 535 |  | $ 18,427
More than 12 months, fair value | 15,571 |  | 15,571 |  | 0
Total, fair value | 16,106 |  | 16,106 |  | 18,427
Less than 12 months, unrealized losses | 53 |  | 53 |  | 1,731
More than 12 months, unrealized losses | 2,017 |  | 2,017 |  | 0
Total, unrealized losses | $ 2,070 |  | $ 2,070 |  | $ 1,731
Less than 12 months, number of securities | Security | 1 |  | 1 |  | 8
More than 12 months, number of securities | Security | 6 |  | 6 |  | 0
Total, number of securities | Security | 7 |  | 7 |  | 8
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 21,508 |  | $ 21,508 |  | $ 31,980
More than 12 months, fair value | 9,590 |  | 9,590 |  | 0
Total, fair value | 31,098 |  | 31,098 |  | 31,980
Less than 12 months, unrealized losses | 1,202 |  | 1,202 |  | 1,643
More than 12 months, unrealized losses | 1,364 |  | 1,364 |  | 0
Total, unrealized losses | $ 2,566 |  | $ 2,566 |  | $ 1,643
Less than 12 months, number of securities | Security | 5 |  | 5 |  | 9
More than 12 months, number of securities | Security | 4 |  | 4 |  | 0
Total, number of securities | Security | 9 |  | 9 |  | 9
State and Political Subdivisions [Member] |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 110,058 |  | $ 110,058 |  | $ 140,324
More than 12 months, fair value | 0 |  | 0 |  | 0
Total, fair value | 110,058 |  | 110,058 |  | 140,324
Less than 12 months, unrealized losses | 261 |  | 261 |  | 276
More than 12 months, unrealized losses | 0 |  | 0 |  | 0
Total, unrealized losses | $ 261 |  | $ 261 |  | $ 276
Less than 12 months, number of securities | Security | 69 |  | 69 |  | 148
More than 12 months, number of securities | Security | 0 |  | 0 |  | 0
Total, number of securities | Security | 69 |  | 69 |  | 148
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 255,862 |  | $ 255,862 |  | $ 353,837
More than 12 months, fair value | 105,314 |  | 105,314 |  | 735
Total, fair value | 361,176 |  | 361,176 |  | 354,572
Less than 12 months, unrealized losses | 12,094 |  | 12,094 |  | 35,564
More than 12 months, unrealized losses | 23,087 |  | 23,087 |  | 183
Total, unrealized losses | $ 35,181 |  | $ 35,181 |  | $ 35,747
Less than 12 months, number of securities | Security | 3,457 |  | 3,457 |  | 2,362
More than 12 months, number of securities | Security | 604 |  | 604 |  | 5
Total, number of securities | Security | 4,061 |  | 4,061 |  | 2,367
Mortgage-backed Securities-Residential [Member] |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 7,537 |  | $ 7,537 |  | $ 29,872
More than 12 months, fair value | 19,159 |  | 19,159 |  | 0
Total, fair value | 26,696 |  | 26,696 |  | 29,872
Less than 12 months, unrealized losses | 687 |  | 687 |  | 3,289
More than 12 months, unrealized losses | 3,642 |  | 3,642 |  | 0
Total, unrealized losses | $ 4,329 |  | $ 4,329 |  | $ 3,289
Less than 12 months, number of securities | Security | 21 |  | 21 |  | 27
More than 12 months, number of securities | Security | 9 |  | 9 |  | 0
Total, number of securities | Security | 30 |  | 30 |  | 27
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 24,620 |  | $ 24,620 |  | $ 39,865
More than 12 months, fair value | 11,189 |  | 11,189 |  | 0
Total, fair value | 35,809 |  | 35,809 |  | 39,865
Less than 12 months, unrealized losses | 1,808 |  | 1,808 |  | 2,242
More than 12 months, unrealized losses | 1,913 |  | 1,913 |  | 0
Total, unrealized losses | $ 3,721 |  | $ 3,721 |  | $ 2,242
Less than 12 months, number of securities | Security | 30 |  | 30 |  | 27
More than 12 months, number of securities | Security | 3 |  | 3 |  | 0
Total, number of securities | Security | 33 |  | 33 |  | 27
Mortgage-backed Securities-Multi-family [Member] |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 7,920 |  | $ 7,920 |  | $ 71,631
More than 12 months, fair value | 63,711 |  | 63,711 |  | 12,078
Total, fair value | 71,631 |  | 71,631 |  | 83,709
Less than 12 months, unrealized losses | 1,118 |  | 1,118 |  | 12,868
More than 12 months, unrealized losses | 18,494 |  | 18,494 |  | 2,776
Total, unrealized losses | $ 19,612 |  | $ 19,612 |  | $ 15,644
Less than 12 months, number of securities | Security | 4 |  | 4 |  | 29
More than 12 months, number of securities | Security | 27 |  | 27 |  | 5
Total, number of securities | Security | 31 |  | 31 |  | 34
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 75,500 |  | $ 75,500 |  | $ 155,726
More than 12 months, fair value | 63,806 |  | 63,806 |  | 0
Total, fair value | 139,306 |  | 139,306 |  | 155,726
Less than 12 months, unrealized losses | 6,316 |  | 6,316 |  | 13,895
More than 12 months, unrealized losses | 14,479 |  | 14,479 |  | 0
Total, unrealized losses | $ 20,795 |  | $ 20,795 |  | $ 13,895
Less than 12 months, number of securities | Security | 40 |  | 40 |  | 68
More than 12 months, number of securities | Security | 22 |  | 22 |  | 0
Total, number of securities | Security | 62 |  | 62 |  | 68
Corporate Debt Securities [Member] |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 14,903 |  | $ 14,903 |  | $ 16,634
More than 12 months, fair value | 1,157 |  | 1,157 |  | 0
Total, fair value | 16,060 |  | 16,060 |  | 16,634
Less than 12 months, unrealized losses | 1,497 |  | 1,497 |  | 1,250
More than 12 months, unrealized losses | 343 |  | 343 |  | 0
Total, unrealized losses | $ 1,840 |  | $ 1,840 |  | $ 1,250
Less than 12 months, number of securities | Security | 13 |  | 13 |  | 16
More than 12 months, number of securities | Security | 2 |  | 2 |  | 0
Total, number of securities | Security | 15 |  | 15 |  | 16
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |  |  |
Less than 12 months, fair value | $ 5,998 |  | $ 5,998 |  | $ 10,751
More than 12 months, fair value | 6,417 |  | 6,417 |  | 0
Total, fair value | 12,415 |  | 12,415 |  | 10,751
Less than 12 months, unrealized losses | 602 |  | 602 |  | 651
More than 12 months, unrealized losses | 876 |  | 876 |  | 0
Total, unrealized losses | $ 1,478 |  | $ 1,478 |  | $ 651
Less than 12 months, number of securities | Security | 5 |  | 5 |  | 11
More than 12 months, number of securities | Security | 8 |  | 8 |  | 0
Total, number of securities | Security | 13 |  | 13 |  | 11

X
- References No definition available. + Details
Name: | gcbc_AvailableForSaleAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionAbstract
Namespace Prefix: | gcbc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition This item represents the net carrying amount of the transferred security to another category of investments i.e. value transferred from available for sale to held to maturity. + References No definition available. + Details
Name: | gcbc_AvailableForSaleSecuritiesTransfersToHeldToMaturity
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Number of investment positions in held-to-maturity investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | gcbc_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
Namespace Prefix: | gcbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investment positions in held-to-maturity investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | gcbc_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
Namespace Prefix: | gcbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of debt securities sold which are classified as available-for-sale securities during the period. + References No definition available. + Details
Name: | gcbc_NumberOfDebtSecuritiesAvailableForSale
Namespace Prefix: | gcbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of investment positions in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | gcbc_NumberOfSecuritiesUnrealizedLossPosition
Namespace Prefix: | gcbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investment positions in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | gcbc_NumberOfSecuritiesUnrealizedLossPositionLessThanTwelveMonths
Namespace Prefix: | gcbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investment positions that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | gcbc_NumberOfSecuritiesUnrealizedLossPositionTwelveMonthsOrLonger
Namespace Prefix: | gcbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item represents the excess of amortized cost basis over fair value of securities in a continuous loss position for 12 months or greater. + References No definition available. + Details
Name: | gcbc_SecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the excess of amortized cost basis over fair value of securities in a continuous loss position for less than 12 months. + References No definition available. + Details
Name: | gcbc_SecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities in a continuous loss position for less than twelve months. + References No definition available. + Details
Name: | gcbc_SecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities in a continuous loss position for a period greater than 12 months. + References No definition available. + Details
Name: | gcbc_SecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position. + References No definition available. + Details
Name: | gcbc_SecuritiesContinuousUnrealizedLossPositionsAccumulatedLoss
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities that have been in a continuous unrealized loss position. + References No definition available. + Details
Name: | gcbc_SecuritiesContinuousUnrealizedLossPositionsFairValue
Namespace Prefix: | gcbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionQualitativeDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 55 -Paragraph 8 -URI https://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 55 -Paragraph 8 -URI https://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of realized gain (loss) on 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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27357-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 55 -Paragraph 8 -URI https://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(2) -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=126970911&loc=SL120269820-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27337-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI https://asc.fasb.org/extlink&oid=124260329&loc=SL6284422-111562 + Details
Name: | us-gaap_OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of cash inflow from sale 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26853-111562 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 11 -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3151-108585 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=gcbc_MortgageBackedSecuritiesMultiFamilyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |