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Savings Plan (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 1998 | Dec. 31, 1997
Savings Plan [Line Items] |  |  |  |  |
Charges recognized | $ 3,500,000 | $ 3,200,000 | $ 3,000,000 |  |
Number of common stock purchased |  |  |  | 7,200 | 46,671
Amount of common stock purchased |  |  |  | $ 200,000 | $ 1,000,000
Savings Plan |  |  |  |  |
Savings Plan [Line Items] |  |  |  |  |
Employee contribution to savings plan | 1 |  |  |  |
Defined Contribution Plan Employer Employee Contribution | $ 1 |  |  |  |
Maximum matching contribution | 5.00% |  |  |  |
Percentage of enrollment of base pay | 3.00% |  |  |  |
Nonqualified Plan [Member] |  |  |  |  |
Savings Plan [Line Items] |  |  |  |  |
Liability under the restoration plan | $ 1,300,000 | $ 1,600,000 |  |  |
Liability under the restoration plan, shares | 65,548 | 67,013 |  |  |

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- Definition Common stock shares purchased for employee trust. + References No definition available. + Details
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- Definition Common stock shares purchased for employee trust shares. + References No definition available. + Details
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- Definition Percentage of employee salary contributions to defined contribution plan unless elected otherwise per terms of Company's defined contribution benefit plan. + References No definition available. + Details
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- Definition Defined Contribution Plan Employer Employee Contribution + References No definition available. + Details
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- Definition Defined contribution plan employer employee match. + References No definition available. + Details
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- Definition Liability under restoration benefit plan. + References No definition available. + Details
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- Definition Savings plan [line items] + References No definition available. + Details
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- Definition Shares held by restoration plan. + References No definition available. + Details
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Balance Type: | na
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Details
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- Details
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Period Type: |