CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Income	$ 204,554	$ 253,562	$ 259,624
Cash flow hedges:
Total cash flow hedges	(32,018)	35,864	51,999
Pension and postretirement plans:
Amortization of net obligation at transition, net of taxes of $112, $100 and $96, respectively	207	186	177
Amortization of prior service cost, net of taxes of $90, $119 and $104, respectively	167	221	194
Amortization of net loss, net of taxes of $4,472, $1,676 and $1,270, respectively	8,306	3,113	2,359
Current period change in fair value of pension and postretirement plans, net of taxes of $6,237, ($9,393), and ($5,699), respectively	11,582	(17,443)	(10,584)
Total pension and postretirement plans	20,262	(13,923)	(7,854)
Comprehensive Income	192,798	275,503	303,769
Commodity Contract
Cash flow hedges:
Reclassification adjustment for derivative instruments, net of tax	(10,866)	66,438	67,547
Reclassification adjustment for derivative instruments, net of tax	(22,124)	(29,359)	(14,607)
Interest Rate Swap
Cash flow hedges:
Reclassification adjustment for derivative instruments, net of tax	(148)	(2,281)	(941)
Reclassification adjustment for derivative instruments, net of tax	$ 1,120	$ 1,066	$ 0