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Employee Benefits - Employee Benefits (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Contribution Plan Wage Base | $ 270,000 | $ 265,000 | $ 265,000
Deferred Compensation Arrangement with Individual, Requisite Service Period | 3 years |  |
Defined Contribution Plan, Cost | $ 1,500,000 | $ 1,300,000 | $ 1,200,000
Deferred Compensation Arrangement with Individual, Compensation Expense | $ 100,000 |  |
Base Percentage [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contribution percentage to retirement plan | 13.20% |  |
Excess Percentage for amounts above Social Security taxable wage base] [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contribution percentage to retirement plan | 5.70% |  |
Nonqualified Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contribution percentage to retirement plan | 18.90% |  |

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- Definition Employer contribution percentage to retirement plan + References No definition available. + Details
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- Definition The compensation expense recognized during the period pertaining to the deferred compensation arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 30 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363 + Details
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- Definition Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6409961&loc=d3e20487-108367 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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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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