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Stock Based Compensation (Schedule of Outstanding Stock Options) (Details) - $ / shares | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 212,725 | 225,669 | 276,807 | 294,720
Average Exercise Price | $ 20.76 | $ 19.46 | $ 17.94 | $ 17.83
Remaining Life, Years | 6 years 1 month 6 days |  |  |
Options Exercisable | 177,975 | 216,644 | 270,032 |
Average Exercise Price | $ 18.41 | $ 17.59 | $ 17.85 |
Average Exercise Price - $16.67 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 9,075 |  |  |
Average Exercise Price | $ 16.67 |  |  |
Remaining Life, Years | 1 year |  |  |
Options Exercisable | 9,075 |  |  |
Average Exercise Price | $ 16.67 |  |  |
Average Exercise Price - $17.33 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 17,325 |  |  |
Average Exercise Price | $ 17.33 |  |  |
Remaining Life, Years | 2 years |  |  |
Options Exercisable | 17,325 |  |  |
Average Exercise Price | $ 17.33 |  |  |
Average Exercise Price - $16.83 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 15,675 |  |  |
Average Exercise Price | $ 16.83 |  |  |
Remaining Life, Years | 3 years |  |  |
Options Exercisable | 15,675 |  |  |
Average Exercise Price | $ 16.83 |  |  |
Average Exercise Price - $16.65 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 20,625 |  |  |
Average Exercise Price | $ 16.65 |  |  |
Remaining Life, Years | 4 years |  |  |
Options Exercisable | 20,625 |  |  |
Average Exercise Price | $ 16.65 |  |  |
Average Exercise Price - $18.03 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 29,700 |  |  |
Average Exercise Price | $ 18.03 |  |  |
Remaining Life, Years | 5 years |  |  |
Options Exercisable | 29,700 |  |  |
Average Exercise Price | $ 18.03 |  |  |
Average Exercise Price - $18.36 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 1,650 |  |  |
Average Exercise Price | $ 18.36 |  |  |
Remaining Life, Years | 5 years |  |  |
Options Exercisable | 1,650 |  |  |
Average Exercise Price | $ 18.36 |  |  |
Average Exercise Price - $19.30 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 3,000 |  |  |
Average Exercise Price | $ 19.30 |  |  |
Remaining Life, Years | 5 years 9 months 18 days |  |  |
Options Exercisable | 3,000 |  |  |
Average Exercise Price | $ 19.30 |  |  |
Average Exercise Price - $17.93 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 26,925 |  |  |
Average Exercise Price | $ 17.93 |  |  |
Remaining Life, Years | 6 years |  |  |
Options Exercisable | 26,925 |  |  |
Average Exercise Price | $ 17.93 |  |  |
Average Exercise Price - $19.39 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 14,250 |  |  |
Average Exercise Price | $ 19.39 |  |  |
Remaining Life, Years | 6 years 10 months 24 days |  |  |
Options Exercisable | 14,250 |  |  |
Average Exercise Price | $ 19.39 |  |  |
Average Exercise Price - $19.03 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 16,500 |  |  |
Average Exercise Price | $ 19.03 |  |  |
Remaining Life, Years | 7 years 10 months 24 days |  |  |
Options Exercisable | 16,500 |  |  |
Average Exercise Price | $ 19.03 |  |  |
Average Exercise Price - $22.37 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 23,250 |  |  |
Average Exercise Price | $ 22.37 |  |  |
Remaining Life, Years | 9 years |  |  |
Options Exercisable | 23,250 |  |  |
Average Exercise Price | $ 22.37 |  |  |
Average Exercise Price - $32.81 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options Outstanding | 34,750 |  |  |
Average Exercise Price | $ 32.81 |  |  |
Remaining Life, Years | 10 years |  |  |
Options Exercisable | 0 |  |  |
Average Exercise Price | $ 0.00 |  |  |

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- Definition The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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