Loans - Troubled Debt Restructurings (Details 10) $ in Thousands	9 Months Ended
Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of contracts \| contract	7	5
Pre-modification outstanding recorded investment	$ 7,074	$ 700
Recorded investment	6,303	$ 152
Allowance for loan losses, troubled debt restructurings	84
Troubled debt restructuring	$ 200
Commercial & Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts \| contract	6	3
Pre-modification outstanding recorded investment	$ 1,657	$ 545
Recorded investment	$ 886
Consumer and other [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts \| contract		1
Pre-modification outstanding recorded investment		$ 125
Recorded investment		$ 123
Construction, land & land development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts \| contract		1
Pre-modification outstanding recorded investment		$ 30
Recorded investment		$ 29
Commerical real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts \| contract	1
Pre-modification outstanding recorded investment	$ 5,417
Recorded investment	$ 5,417

Represents the amount of loans that have been modified in a troubled debt restructuring.

No definition available.

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

- Definition

Amount of allowance for credit losses related to receivables which had been measured under a general allowance for credit losses methodology that are now identified as troubled debt restructurings.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

+ Details

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Period Type:	instant

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- Details

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- Details

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