Financial Instruments and Risk Management (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) contract $ / bbl	Dec. 31, 2017 USD ($) bbl / d contract
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of foreign currency derivatives | contract	0	0
Amount of loss reclassified to interest expense	$ 2,963	$ 2,963
Amount of loss expected to be reclassified to interest expense in the next 12 months	3,000
Loss deferred for fair value of interest rate derivative contracts, net of tax	7,900
Income taxes on deferred loss on fair value of interest rate derivative contracts	$ 2,100
Commodity Derivative Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day) | bbl / d		21,000
Average price | $ / bbl	54.88