CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Pension and retiree medical benefits:
Amortization of losses (gains) included in net periodic benefit cost, tax	$ 550	$ 2,503
Derivative instruments:
Net fair value (decrease) increase, tax	(5)	12
Reclassification of losses (gains) to net income, tax	358	1,429
Marketable securities:
Net fair value increase (decrease), tax	$ 24	$ (18)

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Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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