CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, tax	$ 567	$ 686	$ 1,666	$ 3,918
Derivative instruments:
Net fair value increase (decrease), tax	(27)	14	(22)	(2)
Reclassification of losses to net income, tax	393	266	1,115	2,145
Marketable securities:
Net fair value increase (decrease), tax	$ 1	$ 73	$ 26	$ 56