CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Comprehensive income:
Net income	$ 196,857	$ 183,060	$ 433,427	$ 366,953
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $729, $647, $3,232 and $1,269, respectively	1,135	932	496	1,827
Derivative instruments:
Net fair value decrease, net of tax of $(29), $(23,164), $(17) and $(6,673), respectively	(44)	(35,727)	(31)	(10,335)
Reclassification of losses to net income, net of tax of $451, $158, $1,881 and $314, respectively	694	182	389	363
Total derivative instruments, net of tax	650	(35,545)	358	(9,972)
Marketable securities:
Net fair value increase (decrease), net of tax of $0, $83, $(18) and $119, respectively	0	122	(36)	174
Other comprehensive income (loss)	1,785	(34,491)	818	(7,971)
Comprehensive income	$ 198,642	$ 148,569	$ 434,245	$ 358,982