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Financial Instruments (Narrative) (Details) $ in Thousands | 1 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Aug. 31, 2017 USD ($) a | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Number of acres | a | 6 |  |  |
Proceeds from sale of property, plant, and equipment | $ 12,200 |  |  |
Promissory note received in sale of property, plant, and equipment | $ 5,700 |  |  |
Stated interest rate on promissory note | 3.50% |  |  |
Gain on sale of land | $ 3,300 | $ 0 | $ 3,307 |
Borrowings [Member] | Unsecured debt [Member] | Level 2 [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Unsecured notes |  | $ 375,000 |  | $ 375,000

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