Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Pension Plans [Member]	Dec. 31, 2012 Pension Plans [Member]	Dec. 31, 2011 Pension Plans [Member]	Dec. 31, 2013 Post-Retirement Plans [Member]	Dec. 31, 2012 Post-Retirement Plans [Member]	Dec. 31, 2011 Post-Retirement Plans [Member]	Dec. 31, 2013 Derivative [Member]	Dec. 31, 2012 Derivative [Member]	Dec. 31, 2011 Derivative [Member]	Dec. 31, 2010 Derivative [Member]
Schedule of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ (117,287)	$ (103,047)	$ (46,234)	$ (121,602)	$ (110,626)	$ (54,325)	$ 4,277	$ 7,504	$ 10,761	$ 9	$ 38	$ 75	$ (2,670)
Other comprehensive income (loss) before reclassifications:
Actuarial gain (loss) for retiree liabilities	130,330	(27,350)	(91,523)	129,856	(27,518)	(91,715)	474	168	192
Unrealized gain (loss) for derivative instruments			631
Amounts reclassified from accumulated other comprehensive income:
Actuarial costs (reclassified to salaries, wages and benefits)	12,715	11,114	2,911	12,296	10,681	2,700	419	433	211
Negative prior service cost (reclassified to salaries, wages and benefits)	(5,654)	(5,552)	(5,552)				(5,654)	(5,552)	(5,552)
Hedging gain (reclassified to interest expense)	(50)	(57)	(223)
Unrealized loss on derivative instruments			3,932
Income Tax (Expense) or Benefit				(51,622)	5,861	32,714	1,729	1,724	1,892
Income Tax (Expense) or Benefit	21	20	(1,595)
Income Tax (Expense) or Benefit	(49,872)	7,605	33,011
Other comprehensive income (loss), net of tax				90,530	(10,976)	(56,301)	(3,032)	(3,227)	(3,257)
Other comprehensive income (loss), net of tax	(29)	(37)	2,745
Other comprehensive income (loss), net of tax	87,469	(14,240)	(56,813)
Accumulated other comprehensive income (loss), ending balance	$ (29,818)	$ (117,287)	$ (103,047)	$ (31,072)	$ (121,602)	$ (110,626)	$ 1,245	$ 4,277	$ 7,504	$ 9	$ 38	$ 75	$ (2,670)