Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Net Income	$ 21,109us-gaap_NetIncomeLoss	$ 17,681us-gaap_NetIncomeLoss
Employee Benefits, net of tax:
Amortization of prior service cost, net of tax of $(7), $(6), respectively	(10)	(9)
Net gain, net of tax of $62 and $27, respectively	92	40
Commodity Contract Cash Flow Hedges [Abstract]
Unrealized gain on commodity contract cash flow hedges, net of tax of $17 and $0, respectively.	26	0
Total other comprehensive income	108	31
Comprehensive Income	$ 21,217us-gaap_ComprehensiveIncomeNetOfTax	$ 17,712us-gaap_ComprehensiveIncomeNetOfTax

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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- Definition

Amount after tax of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

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- Definition

Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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