Represents the balance of nonaccrual loans excluding nonaccrual restructured loans.

No definition available.

Name:	gnbc_NonaccrualLoansExcludingRestructuredLoans
Namespace Prefix:	gnbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the balance of nonaccrual loans that have been restructured.

+ References

No definition available.

+ Details

Name:	gnbc_NonaccrualLoansRestructured
Namespace Prefix:	gnbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents all of the loans classified as nonperforming by the reporting entity, including but not limited to nonaccrual loans, accruing loans past due 90 days or more, and accruing and nonaccruing restructured loans.

+ References

No definition available.

+ Details

Name:	gnbc_NonperfomringLoans
Namespace Prefix:	gnbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the balance of restructured loans that are still accruing.

+ References

No definition available.

+ Details

Name:	gnbc_RestructuredLoansAccruing
Namespace Prefix:	gnbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestmentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethodAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=gnbc_ReservedBasedEnergyLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=gnbc_EnergyRelatedServiceIndustryLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Impaired Loans Summary (Details 7) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Impaired loans summary
Nonaccrual loans	$ 22,762		$ 22,762		$ 2,127
Accruing loans past due 90 days or more	4,233		4,233		16
Restructured loans - nonaccrual	1,623		1,623		2,717
Restructured loans - accruing	6,048		6,048		2,257
Total nonperforming loans	34,666		34,666		7,117
Impaired loans, other infomation
Total nonaccrual loans	24,400		24,400		$ 4,800
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	83	$ 115	313	$ 70
Reserved Based Energy Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	18,300		18,300
Energy Related Service Industry Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 400		$ 400