Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Pension Plans [Member]	Jun. 30, 2013 Pension Plans [Member]	Jun. 30, 2014 Pension Plans [Member]	Jun. 30, 2013 Pension Plans [Member]	Jun. 30, 2014 Post-Retirement Plans [Member]	Jun. 30, 2013 Post-Retirement Plans [Member]	Jun. 30, 2014 Post-Retirement Plans [Member]	Jun. 30, 2013 Post-Retirement Plans [Member]	Jun. 30, 2014 Derivative [Member]	Mar. 31, 2014 Derivative [Member]	Dec. 31, 2013 Derivative [Member]	Jun. 30, 2013 Derivative [Member]	Mar. 31, 2013 Derivative [Member]	Dec. 31, 2012 Derivative [Member]
Schedule of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ (30,330)	$ (116,171)	$ (29,818)	$ (117,287)	$ (31,073)	$ (119,644)	$ (31,072)	$ (121,602)	$ 741	$ 3,443	$ 1,245	$ 4,277	$ (5)	$ 2	$ 9	$ 22	$ 30	$ 38
Amounts reclassified from accumulated other comprehensive income:
Actuarial costs (reclassified to salaries, wages and benefits)	80	3,178	159	6,356	0	3,074	(1)	6,148	80	104	160	208
Negative prior service cost (reclassified to salaries, wages and benefits)	(872)	(1,413)	(1,744)	(2,826)					(872)	(1,413)	(1,744)	(2,826)
Hedging gain (reclassified to interest expense)	(11)	(13)	(22)	(26)
Income Tax (Expense) or Benefit					0	(1,116)	0	(2,232)	288	475	576	950
Income Tax (Expense) or Benefit	4	5	8	10
Income Tax (Expense) or Benefit	292	(636)	584	(1,272)
Other comprehensive income (loss), net of tax					0	1,958	(1)	3,916	(504)	(834)	(1,008)	(1,668)
Other comprehensive income (loss), net of tax	(7)	(8)	(14)	(16)
Other comprehensive income (loss), net of tax	(511)	1,116	(1,023)	2,232
Accumulated other comprehensive income (loss), ending balance	$ (30,841)	$ (115,055)	$ (30,841)	$ (115,055)	$ (31,073)	$ (117,686)	$ (31,073)	$ (117,686)	$ 237	$ 2,609	$ 237	$ 2,609	$ (5)	$ 2	$ 9	$ 22	$ 30	$ 38