| **Off-Balance Sheet Arrangements**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| **Off-Balance Sheet Arrangements [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Off-Balance Sheet Arrangements                | Off-Balance Sheet ArrangementsIn the normal course of business, various commitments are outstanding that are not reflected in the consolidated financial statements. Significant commitments at December 31, 2013 are discussed below.Commitments by the Bank to extend credit and undisbursed advances on customer lines of credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. At December 31, 2013, total commitments to extend credit and undisbursed advances on customer lines of credit amounted to $225.6 million. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Since many commitments expire without being fully drawn, the total commitment amounts do not necessarily represent future cash requirements. COB evaluates each customer’s creditworthiness on a case-by-case basis. The amount of collateral obtained, if deemed necessary, upon extension of credit is based on the credit evaluation of the borrower.The Bank issues, and Granite previously issued, standby letters of credit whereby each guarantees the performance of a customer to a third party if a specified triggering event or condition occurs. The guarantees generally expire within one year and may be automatically renewed depending on the terms of the guarantee. All standby letters of credit provide for recourse against the customer on whose behalf the letter of credit was issued, and this recourse may be further secured by a pledge of assets. The maximum potential amount of undiscounted future payments related to standby letters of credit was $0.7 million at December 31, 2013 and $0.9 million at December 31, 2012.The Bank's exposure to credit loss in the event of nonperformance by the other party to the financial instrument for commitments to extend is represented by the contractual notional amount of those instruments. The Bank uses the same credit policies in making commitments and conditional obligations as they do for on-balance-sheet instruments. The fair value of these commitments was not considered material.COB does not have any special purpose entities or other similar forms of off-balance sheet financing. |

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| - Definition
Off-Balance sheet arrangements.
+ References
No definition available.
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