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Derivatives And Risk Management (Interest Rate Swap Agreements) (Details) $ in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 USD ($) Caontracts | Dec. 31, 2017 USD ($) Caontracts
Derivatives, Fair Value [Line Items] |  |
Payments for (proceeds from) settlement of derivative instruments | $ (25,900) |
2018 | Interest Rate Swap [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Number of interest rate swaps settled | Caontracts | 14 |
Number of Interest Rate Derivatives Held | Caontracts |  | 14
Derivative, Notional Amount |  | $ 275,000
Derivative, Maturity Date |  | Dec. 31, 2018
Settled derivative notional amount | $ 275,000 |
2019 | Interest Rate Swap [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Number of Interest Rate Derivatives Held | Caontracts | 6 | 6
Derivative, Notional Amount | $ 70,000 | $ 70,000
Derivative, Maturity Date | Dec. 31, 2019 | Dec. 31, 2019
2020 | Interest Rate Swap [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Number of Interest Rate Derivatives Held | Caontracts | 4 | 3
Derivative, Notional Amount | $ 40,000 | $ 30,000
Derivative, Maturity Date | Dec. 31, 2020 | Dec. 31, 2020
2021 | Interest Rate Swap [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Number of Interest Rate Derivatives Held | Caontracts | 1 | 1
Derivative, Notional Amount | $ 15,000 | $ 15,000
Derivative, Maturity Date | Dec. 31, 2021 | Dec. 31, 2021
2022 | Interest Rate Swap [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Number of Interest Rate Derivatives Held | Caontracts | 5 | 5
Derivative, Notional Amount | $ 60,000 | $ 60,000
Derivative, Maturity Date | Dec. 31, 2022 | Dec. 31, 2022

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Number of interest rate derivative instruments held by the entity at the reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959 + Details
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