Other Real Estate Owned (Expenses Related To Foreclosed Assets) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Accounting Changes and Error Corrections [Abstract]
Net (gain)/loss on sale and valuation adjustments	$ (8)	$ 119
Operating expenses, net of rental income	64	215
Total expenses related to foreclosed assets	$ 56	$ 334

Losses recognized on the sale of other real estate owned combined with write-downs on other real estate owned offset by gains recognized upon sale of these properties.

No definition available.

Name:	gbnk_OtherRealEstateWriteDownsNet
Namespace Prefix:	gbnk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration