ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES - Guaranteed Portion of Loans, Net (Details)	12 Months Ended
Dec. 31, 2017
Minimum
Loan guarantee percentage	50.00%
Maximum
Loan guarantee percentage	90.00%

Represents the percentage of a loan that is typically guaranteed by the reporting entity

No definition available.

Name:	gnbc_LoanGuaranteePercentage
Namespace Prefix:	gnbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration