Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Consolidated Statements of Comprehensive Income
Net income	$ 13,852	$ 9,996
Net unrealized gain (loss) on securities available-for-sale:
Net unrealized holding gain (loss) on securities arising during the period	130	(814)
Reclassification adjustment for gain included in net income		(1,604)
Net unrealized gain (loss) on securities available-for-sale	130	(2,418)
Net actuarial loss adjustment on pension plans and other postretirement benefits:
Net actuarial loss adjustment arising during the period		24,286
Reclassification adjustment for net actuarial loss included in net income	627	2,201
Net actuarial loss adjustment on pension plans and other postretirement benefits	627	26,487
Prior service cost adjustment on pension plans and other postretirement benefits:
Prior service cost adjustment arising during the period		(3,537)
Reclassification adjustment for prior service cost included in net income	34	2
Prior service cost adjustment on pension plans and other postretirement benefits	34	(3,535)
Reclassification adjustment for loss on cash flow hedge included in net income		48
Total other comprehensive income, net of tax	791	20,582
Comprehensive income	$ 14,643	$ 30,578