CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Unrealized gain (loss), net of taxes (benefits)	$ (19,730,000)	$ 15,578,000	$ 15,470,000
Less: reclassificaiton adjustment for net gains realized in net income, net of taxes (benefits)	4,175,000	4,178,000	7,911,000
Changes in market value of derivatives, taxes (benefit)	(59,282,000)	(4,909,000)	1,443,000
Less: reclassification adjustment for net (gains) losses included in net income, net of taxes (benefits)	475,000	907,000	(736,000)
Recognition of actuarial net gain (loss) from pension and other postretirement plans, taxes (benefit)	$ (11,410,000)	$ (1,392,000)	$ 13,092,000