| Derivative Financial Instruments - Cash Receipts (Payments) on Derivative Settlements, Net Included within Net Cash Provided by Operating Activities (Details) - USD ($) $ in Thousands | 9 Months Ended | |
|---|---|---|
| Sep. 30, 2018 | Sep. 30, 2017 | |
| Derivative Instruments And Hedging Activities Disclosure [Abstract] | ||
| Cash receipts (payments) on derivative settlements, net | $ (3,091) | $ 3,924 | 
| X | ||||||||||
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- References No definition available. 
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| X | ||||||||||
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- Definition Cash proceeds payments on derivative settlements net operating activities. No definition available. 
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