Financial Instruments and Risk Management (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 contract	Dec. 31, 2012	Dec. 31, 2015	Dec. 31, 2013	May 31, 2012
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Accounts receivable for final settlement of WTI contracts	$ 23,168,000
Number of open WTI contracts	0
Repayments Of Notes Payable		350,000,000
Repayments of debt		350,000,000
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 foreign derivative contracts
Fair value of commodity derivative contracts
Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Deferred loss charged to income	2,963,000	1,852,000		2,963,000
Loss deferred for fair value of interest rate derivative contracts, net of tax	21,852,000
Loss deferred for fair value of interest rate derivative contracts	7,648,000
Face amount of notes					350,000,000
Foreign exchange derivative contract [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of foreign derivative contracts	25,000			26,000
Fair value of commodity derivative contracts
Foreign exchange derivative contract [Member] | Currency, U.S. Dollar
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Short-term derivative instruments	$ 21,000,000			$ 32,300,000