Financial Instruments and Risk Management (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) bbl / d	Dec. 31, 2014 USD ($) contract	Dec. 31, 2013 USD ($)	May. 31, 2012 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of open derivative contracts | contract			0
Deferred loss charged to income		$ 2,963,000	$ 2,963,000
Scenario, Forecast [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Deferred loss charged to income	$ 2,963,000
Commodity Derivative Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of commodity derivative contracts
Daily production commitment (barrels per day) | bbl / d		20,000
Gain charged to income		$ 77,300,000
Fair value of foreign derivative contracts
Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Face amount of notes					$ 350,000,000
Deferred loss charged to income		$ 2,963,000	$ 2,963,000	$ 2,963,000
Loss deferred for fair value of interest rate derivative contracts, net of tax		18,889,000
Loss deferred for fair value of interest rate derivative contracts		$ 6,611,000
Foreign Exchange Derivative Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of commodity derivative contracts
Foreign Exchange Derivative Contracts [Member] | Currency, U.S. Dollar
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Short-term derivative instruments		$ 4,800,000	$ 21,000,000
Accounts Payable [Member] | Foreign Exchange Derivative Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of foreign derivative contracts		29,000	25,000
Accounts Receivable [Member] | Commodity Derivative Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of commodity derivative contracts		$ 89,358,000	$ 23,168,000