Organization, Operations And Basis Of Presentation (Narrative) (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) segment $ / shares item shares	Dec. 31, 2017 USD ($) $ / shares	Oct. 27, 2017 USD ($)	Sep. 08, 2016 USD ($)
Organizations Operations And Basis Of Presentation [Line Items]
Purchased credit impaired loans included in loan portfolio	$ 1,060,000	$ 1,060,000
Number of days for an unsecured loan to become delinquent		90 days
Number of days past due before smaller loans trigger charge offs		90 days
Number of portfolio segment loans are designated into \| segment		3
Number of derivative categories \| item		3
Shares authorized for repurchase \| shares	1,000,000	1,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001	$ 0.001	$ 0.001
Federal rate		21.00%	35.00%
Re-measurement of net deferred tax asset			$ 976,000
Deferred tax assets, unrealized loss on securities and interest rate swaps	$ 3,770,000	$ 3,770,000	1,867,000
Deferred Tax Assets, Net	3,586,000	3,586,000	1,802,000
Deferred Tax Assets, Valuation Allowance	0	0	0
Interest and penalties accrued	0	$ 0	0
Uncompleted customer contract liabilities			0
Accounting Standards Update 2014-09 [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Cumulative transittion adjustment on accumulated deficit			$ 0
Accounting Standards Update 2018-02 [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Reclassification of stranded tax effect	$ 1,011,000
Home State Acquisition [Member]
Organizations Operations And Basis Of Presentation [Line Items]
PCI loans, fair value					$ 2,108,000
Castle Rock Bank [Member]
Organizations Operations And Basis Of Presentation [Line Items]
PCI loans, fair value				$ 1,283,000
Independent Bank Group, Inc. [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Shares issuable per share of stock \| $ / shares		$ 0.45
2005 Stock Incentive Plan [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Number of grants authorized \| shares	1,700,000	1,700,000
2015 Stock Incentive Plan [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Number of grants authorized \| shares	935,000	935,000
Shares available for grant under Incentive Plan \| shares	497,975	497,975
Non-Compete Agreements [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Intangible assets, Useful life		3 years
Minimum [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Vesting period		1 year
Minimum [Member] \| Accounting Standards Update 2016-02 [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Estimated impact on assets and liabilities	$ 10,000,000	$ 10,000,000
Minimum [Member] \| Customer Relationship [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Intangible assets, Useful life		10 years
Minimum [Member] \| Core Deposits [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Intangible assets, Useful life		10 years
Maximum [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Vesting period		5 years
Maximum [Member] \| Accounting Standards Update 2016-02 [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Estimated impact on assets and liabilities	$ 12,000,000	$ 12,000,000
Maximum [Member] \| Customer Relationship [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Intangible assets, Useful life		13 years
Maximum [Member] \| Core Deposits [Member]
Organizations Operations And Basis Of Presentation [Line Items]
Intangible assets, Useful life		15 years

Guaranty Bancorp 10-Q