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

The amount of interest income on impaired and nonperforming loans that is due to the change in present value attributable to the passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5278-111524

+ Details

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

- 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) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2015
Impaired loans summary
Nonaccrual loans	$ 49,264			$ 37,541
Accruing loans past due 90 days or more	12,147			52
Restructured loans - nonaccrual	1,270			1,464
Restructured loans - accruing	5,616			5,988
Total nonperforming loans	68,297			45,045
Impaired loans, other infomation
Impaired loans, interest recognized	90		$ 53
Total nonaccrual loans	50,500			$ 39,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	890	$ 164
Reserved Based Energy Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	41,400
Energy Related Service Industry Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 766,000