CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension and other postretirement benefits (Note 8):
Unrealized actuarial loss, net of tax benefit	$ (6,067)	$ (7,738)	$ (4,223)
Amortization to income:
Actuarial loss, net of tax benefit	1,950	1,870	1,705
Prior service cost, tax benefit	179	201	215
Transition obligation, tax benefit	3	59	39
Derivative instruments:
Net unrealized gain (loss), net of tax	(37,389)	(61,348)	(61,329)
Reclassification of net realized (gain) loss to income, net of tax (expense) benefit	$ 46,288	$ 48,453	$ 72,877