CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income	$ 253,562	$ 259,624	$ 290,807
Pension and postretirement plans:
Amortization of net obligation at transition, net of taxes of $100, $96 and $98, respectively	186	177	182
Amortization of prior service cost, net of taxes of $119, $104 and $104, respectively	221	194	194
Amortization of net loss, net of taxes of $1,676, $1,270 and $1,152, respectively	3,113	2,359	2,139
Current period change in fair value of pension and postretirement plans, net of taxes of ($9,393), ($5,699), and ($783), respectively	(17,443)	(10,584)	(1,455)
Total pension and postretirement plans	(13,923)	(7,854)	1,060
Comprehensive Income	275,503	303,769	198,795
Commodity Contract
Other comprehensive income (loss):
Reclassification adjustment for derivative instruments, net of tax	(29,359)	(14,607)	(124,873)
Pension and postretirement plans:
Reclassification adjustment for derivative instruments, net of tax	66,438	67,547	31,801
Interest Rate Swap
Other comprehensive income (loss):
Reclassification adjustment for derivative instruments, net of tax	1,066	0	0
Pension and postretirement plans:
Reclassification adjustment for derivative instruments, net of tax	$ (2,281)	$ (941)	$ 0