CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income	$ 120,686us-gaap_NetIncomeLoss	$ 93,983us-gaap_NetIncomeLoss	$ 98,406us-gaap_NetIncomeLoss
Other comprehensive (loss) income, net of tax:
Reclassification of net gains on derivative instruments to net income	(684)	(730)	(732)
Realized loss on cash flow hedging activities	(11,145)	0	0
Postretirement medical liability adjustment	82	963	(553)
Foreign currency translation	265	166	(54)
Total Other Comprehensive Income (Loss)	(11,482)	399	(1,339)
Comprehensive Income	$ 109,204us-gaap_ComprehensiveIncomeNetOfTax	$ 94,382us-gaap_ComprehensiveIncomeNetOfTax	$ 97,067us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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