Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Accumulated other comprehensive (loss), net of tax [Abstract]
Pension costs. beginning balance	$ (575,163)		$ (349,264)		$ (374,157)
Pension costs, other comprehensive income before reclassifications	(152,402)		(241,064)		(2,301)
Pension costs, amounts reclassified from accumulated other comprehensive loss	29,691		15,165		27,194
Pension costs, net current-period other comprehensive income (loss)	(122,711)		(225,899)		24,893
Pension costs, ending balance	(697,874)		(575,163)		(349,264)
Postretirement costs, beginning balance	(41,811)		(13,369)		(21,554)
Postretirement costs, other comprehensive income before reclassifications	(29,922)		(22,668)		11,424
Postretirement costs, amounts reclassified from accumulated other comprehensive loss	(2,531)		(5,774)		(3,239)
Postretirement plans, net current-period other comprehensive income (loss)	(32,453)		(28,442)		8,185
Postretirement costs, ending balance	(74,264)		(41,811)		(13,369)
Deferred taxes on pension and OPEB costs, beginning balance	230,161		132,752		150,284
Deferred taxes on pension and OPEB costs, other comprehensive income before reclassifications	68,871		100,978		(8,428)
Deferred taxes on pension and OPEB costs, amounts reclassified from accumulated other comprehensive loss	(10,320)		(3,569)		(9,104)
Deferred taxes on pension and OPEB costs, net current-period other comprehensive income (loss)	58,551		97,409		(17,532)
Deferred taxes on pension and OPEB costs, ending balance	288,712		230,161		132,752
All other, beginning balance	(150)		332		(92)
All other, other comprehensive income before reclassifications	0		(482)		424
All other, amounts reclassified from accumulated other comprehensive loss	0		0		0
All other, net current-period other comprehensive income (loss)	0		(482)		424
All other, ending balance	(150)		(150)		332
Accumulated other comprehensive loss, beginning balance	(386,963)		(229,549)		(245,519)
Accumulated other comprehensive loss, other comprehensive (loss) before reclassifications	(113,453)		(163,236)		1,119
Accumulated other comprehensive loss, amounts reclassified from accumulated other comprehensive loss	16,840		5,822		14,851
Accumulated other comprehensive loss, net current-period other comprehensive income (loss)	(96,613)		(157,414)		15,970
Accumulated other comprehensive loss, ending balance	(483,576)		(386,963)		(229,549)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost/credit	199	[1],[2]	199	[1],[2]	199	[1],[2]
Amortization of unrecognized loss	(29,890)	[1],[2]	(15,364)	[1],[2]	(27,393)	[1],[2]
Total before tax	(29,691)	[2]	(15,165)	[2]	(27,194)	[2]
Defined benefit plan, net periodic benefit cost, tax effect	11,282	[2]	5,763	[2]	10,334	[2]
Defined benefit plan, net periodic benefit cost, net of taxes	(18,409)	[2]	(9,402)	[2]	(16,860)	[2]
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost/credit	10,068	[1],[2]	10,198	[1],[2]	8,158	[1],[2]
Amortization of unrecognized loss	(7,537)	[1],[2]	(4,424)	[1],[2]	(4,919)	[1],[2]
Total before tax	2,531	[2]	5,774	[2]	3,239	[2]
Defined benefit plan, net periodic benefit cost, tax effect	(962)	[2]	(2,194)	[2]	(1,230)	[2]
Defined benefit plan, net periodic benefit cost, net of taxes	$ 1,569	[2]	$ 3,580	[2]	$ 2,009	[2]

[1] These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 17 - Retirement Plans for additional details).

[2] Amounts in parentheses indicate debits.