CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, tax	$ 729	$ 647	$ 3,232	$ 1,269
Derivative instruments:
Net fair value decrease, tax	(29)	(23,164)	(17)	(6,673)
Reclassification of losses to net income, tax	451	158	1,881	314
Marketable securities:
Net fair value increase (decrease), tax	$ 0	$ 83	$ (18)	$ 119