Other Comprehensive Income/Loss (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net unrealized loss on securities available-for-sale before tax amount:
Net unrealized holding loss on securities arising during the year	$ (2,040)	$ (5,181)	$ (922)
Reclassification adjustment for gains included in net income	(8,477)
Net unrealized loss on securities available-for-sale	(10,517)
Net actuarial loss adjustment on pension plans and other postretirement benefits before tax amount:
Net actuarial loss adjustment arising during the year	14,141	(55,530)	(25,090)
Reclassification adjustment for net actuarial loss included in net income	5,447	8,592	6,450
Net actuarial loss adjustment on pension plans and other postretirement benefits	19,588	(46,938)	(18,640)
Prior service cost adjustment on pension plans and other postretirement benefits before tax amount:
Prior service cost adjustment arising during the year	(5,463)
Reclassification adjustment for prior service cost included in net income	152	92	146
Prior service cost adjustment on pension plans and other postretirement benefits	(5,311)
Reclassification adjustment for loss on cash flow hedge included in net income, before tax amount	261	330	329
Total other comprehensive income, before tax amount	4,021	(51,697)	(19,087)
Net unrealized loss on securities available-for-sale, tax benefit (expense):
Net unrealized holding loss on securities arising during the year	720	1,827	325
Reclassification adjustment for gains included in net income	2,987
Net unrealized loss on securities available-for-sale	3,707
Net actuarial loss adjustment on pension plans and other postretirement benefits, tax benefit (expense):
Net actuarial loss adjustment arising during the year	(4,998)	19,570	8,843
Reclassification adjustment for net actuarial loss included in net income	(1,920)	(3,028)	(2,273)
Net actuarial loss adjustment on pension plans and other postretirement benefits	(6,918)	16,542	6,570
Prior service cost adjustment on pension plans and other postretirement benefits, tax benefit (expense):
Prior service cost adjustment arising during the year	1,925
Reclassification adjustment for prior service cost included in net income	(54)	(32)	(51)
Prior service cost adjustment on pension plans and other postretirement benefits	1,871
Reclassification adjustment for loss on cash flow hedge included in net income, tax benefit (expense)	(110)	(140)	(139)
Total other comprehensive income, tax benefit (expense)	(1,450)	18,197	6,705
Net unrealized loss on securities available-for-sale:
Net unrealized holding loss on securities arising during the year	(1,320)	(3,354)	(597)
Reclassification adjustment for gains included in net income	(5,490)
Net unrealized loss on securities available-for-sale	(6,810)	(3,354)	(597)
Net actuarial loss adjustment on pension plans and other postretirement benefits:
Net actuarial loss adjustment arising during the year	9,143	(35,960)	(16,247)
Reclassification adjustment for net actuarial loss included in net income	3,527	5,564	4,177
Net actuarial loss adjustment on pension plans and other postretirement benefits	12,670	(30,396)	(12,070)
Prior service cost adjustment on pension plans and other postretirement benefits:
Prior service cost adjustment arising during the year	(3,538)
Reclassification adjustment for prior service cost included in net income	98	60	95
Prior service cost adjustment on pension plans and other postretirement benefits	(3,440)
Reclassification adjustment for loss on cash flow hedge included in net income	151	190	190
Total other comprehensive income (loss), net of tax	$ 2,571	$ (33,500)	$ (12,382)