CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY AND COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Increase (Decrease) in Stockholders' Equity
Pension and retiree medical benefit adjustments, tax	$ (2,247)	$ (1,416)	$ (2,203)
Net derivative instrument changes, tax	(24,488)	(1,208)	4,224
Unrealized gain (loss) - marketable securities, tax	$ (63)	$ 89	$ 284