| **Investment Securities**                              | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               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| **Investments, Debt and Equity Securities [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         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| Investment Securities                                  | Investment SecuritiesOur primary objective in managing the investment portfolio is to maintain a portfolio of high quality, highly liquid investments yielding competitive returns.  We are required under federal regulations to maintain adequate liquidity to ensure safe and sound operations.  We maintain investment balances based on a continuing assessment of cash flows, the level of loan production, current interest rate risk strategies and an assessment of the potential future direction of market interest rate changes.  Investment securities differ in terms of default, interest rate, liquidity and expected rate of return risks.The following table summarizes the amortized cost and estimated fair value of investment securities and presents the related gross unrealized gains and losses:December 31, 2013        (dollars in thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair ValueAvailable-for-Sale:        Obligations of:        U.S. government sponsored enterprises $2,051 $26 $— $2,077Residential mortgage-backed securities-GSE 364,513 974 24,340 341,147Residential mortgage-backed securities-Private 19,770 982 — 20,752Commercial mortgage backed securities-GSE 22,767 — 1,328 21,439Commercial mortgage-backed securities-Private 10,408 — 823 9,585Business Development Company investment 1,753 984 — 2,737Corporate notes 16,795 82 — 16,877Total available-for-sale $438,057 $3,048 $26,491 $414,614Held-to-Maturity:        Residential mortgage-backed securities-GSE 141,724 — 9,907 131,817Commercial mortgage-backed securities-Private 10,071 — 763 9,308     Total held-to-maturity $151,795 $— $10,670 $141,125Total investment securities $589,852 $3,048 $37,161 $555,739         December 31, 2012        (dollars in thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair ValueAvailable-for-Sale:        Obligations of:        U.S. Treasury and government agencies $6,646 $335 $— $6,981U.S. government sponsored enterprises 22,118 55 — 22,173States and political subdivisions 5,918 120 — 6,038Residential mortgage-backed securities-GSE 436,344 5,678 948 441,074Residential mortgage-backed securities-Private 22,649 750 454 22,945Commercial mortgage backed securities-GSE 23,150 209 — 23,359Commercial mortgage backed securities-Private 5,283 34 — 5,317Corporate notes 36,710 270 17 36,963Total $558,818 $7,451 $1,419 $564,850As a member of the Federal Home Loan Bank of Atlanta (“FHLB”), the Bank is required to own capital stock in the FHLB based generally upon the balances of total assets and FHLB advances.  FHLB capital stock is pledged to secure FHLB advances.  This investment is carried at cost since no ready market exists for FHLB stock and there is no quoted market value.  However, redemption of this stock has historically been at par value.  The Bank owned a total of $5.9 million of FHLB stock at December 31, 2013 and $6.3 million at December 31, 2012.  Due to the redemption provisions of FHLB stock, we estimate that fair value approximates cost and that this investment is not impaired at December 31, 2013.  FHLB stock is included in other assets at its original cost basis.As a member bank of the Federal Reserve Bank of Richmond (“FRBR”), the Bank also is required to own capital stock of the FRBR based upon a percentage of the bank's common stock and surplus.  This investment is carried at cost since no ready market exists for FRBR stock and there is no quoted market value.  At December 31, 2013 and December 31, 2012, the Bank owned a total of $4.3 million and $3.1 million of FRBR stock, respectively.  Due to the nature of this investment in an entity of the U.S. government, we have estimated that fair value approximated the cost and that this investment was not impaired at December 31, 2013.  FRBR stock is included in other assets at its original cost basis.Other investments are recorded at cost are included in Other Assets on the Consolidated Balance Sheets, and are composed of the following: (dollars in thousands) December 31,  2013 2012Federal Home Loan Bank stock $5,878 $6,254Federal Reserve Bank stock 4,264 3,087Other investments — 1Total other investments $10,142 $9,342Gross gains and losses recognized (by specific identification) on the sale of securities are summarized as follows:(dollars in thousands) Years Ended December 31,  2013 2012 2011Proceeds from sales of investment securities $177,826 $212,609 $290,491       Gains on sales of investment securities available-for-sale 2,953 4,501 7,400Losses on sales of investment securities available-for-sale (181) (380) (102)Total securities gains, net $2,772 $4,121 $7,298At December 31, 2013, $91.2 million of the investment securities portfolio was pledged to secure public deposits, $18.8 million was pledged to retail repurchase agreements and $77.4 million was pledged to others, principally the FHLB and FRBR, leaving $376.3 million available as unpledged securities collateral. At December 31, 2012, $111.4 million of the investment securities portfolio was pledged to secure public deposits and $6.1 million was pledged to others, leaving $447.3 million available as lendable collateral.The following tables show our investments' estimated fair value and gross unrealized losses, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at December 31, 2013 and December 31, 2012.  The change in unrealized losses during the years ending December 31, 2013 and 2012 was attributed to changes in interest rates and not to changes in the credit quality of these securities. All unrealized losses on investment securities are considered by management to be temporary given the credit quality of these investment securities or the short duration of the unrealized loss, or both. Less than 12 Months 12 Months or More Total(dollars in thousands)Estimated Fair ValueGross Unrealized Losses Estimated Fair ValueGross Unrealized Losses Estimated Fair ValueGross Unrealized LossesDecember 31, 2013        Available-for-Sale:        Residential mortgage-backed securities-GSE$222,475$16,585 $76,501$7,755 $298,976$24,340Residential mortgage-backed securities-Private—— —— ——Commercial mortgage-backed securities-GSE—— 21,4391,328 21,4391,328Commercial mortgage-backed securities-Private9,585823 —— 9,585823Total available-for-sale$232,060$17,408 $97,940$9,083 $330,000$26,491Held-to-Maturity:        Residential mortgage-backed securities-GSE$131,817$9,907 $—$— $131,817$9,907Commercial mortgage-backed securities-Private9,308763 —— 9,308763Total held-to-maturity$141,125$10,670 $—$— $141,125$10,670Total$373,185$28,078 $97,940$9,083 $471,125$37,161         December 31, 2012        Residential mortgage-backed securities-GSE$123,489$904 $7,027$44 $130,516$948Residential mortgage-backed securities-Private6,482438 1,01716 7,499454Corporate notes—— 3,24917 3,24917Total$129,971$1,342 $11,293$77 $141,264$1,419At December 31, 2013, there were 10 investment securities that had continuous unrealized losses for more than twelve months. At December 31, 2012, there were 4 investment securities that had continuous unrealized losses for more than twelve months. The unrealized losses relate to fixed-rate debt securities that have incurred fair value reductions due to higher market interest rates and, for certain securities, increased credit spreads since the respective purchase date. The unrealized losses are not likely to reverse unless and until market interest rates and credit spreads decline to the levels that existed when the securities were purchased. Unrealized losses for all investment securities are reviewed to determine whether the losses are other than temporary. Investment securities are evaluated on at least a quarterly basis and more frequently when economic or market conditions warrant such an evaluation to determine whether a decline in their value below amortized cost is other than temporary. In conducting this assessment, COB evaluates a number of factors including, but not limited to:•How much fair value has declined below amortized cost;•How long the decline in fair value has existed;•The financial condition of the issuer;•Contractual or estimated cash flows of the security;•Underlying supporting collateral;•Past events, current conditions, forecasts;•Significant rating agency changes on the issuer; and•COB’s intent and ability to hold the security for a period of time sufficient to allow for any anticipated recovery in fair value.COB analyzed its securities portfolio at December 31, 2013, and considered ratings, fair value, cash flows and other factors to determine if any of the securities were other than temporarily impaired. Since none of the unrealized losses relate to the marketability of the securities or the issuer’s ability to honor redemption obligations, and COB has determined that it is not more likely than not that COB will be required to sell the security before recovery of its amortized cost basis, none of the securities are deemed to be other than temporarily impaired.The aggregate amortized cost and fair value of securities at December 31, 2013, by remaining contractual maturity, are shown in the following table.  Actual expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations.  Available-for-Sale Held-to-Maturity(dollars in thousands) Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair ValueDue in one year or less $8,404 $8,406 $— $—Due after one year through five years 10,442 10,548 — —Due after five years through 10 years — — — —With no stated maturity 1,753 2,737 — —Total 20,599 21,691 — —Mortgage-backed securities 417,458 392,923 151,795 141,125Total $438,057 $414,614 $151,795 $141,125 |

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| - Definition
The entire disclosure for  investments in certain debt and equity securities.
+ References
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