CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 66,593	$ 53,091	$ 67,209
Net unrealized loss on securities available-for-sale:
Net unrealized holding loss on securities arising during the year	(10,485)	(1,320)	(3,354)
Reclassification adjustment for gain on sales of securities included in net income	(1,332)	(5,490)
Net unrealized loss on securities available-for-sale	(11,817)	(6,810)	(3,354)
Net actuarial loss adjustment on pension plans and other postretirement benefits:
Net actuarial loss adjustment arising during the year	44,180	9,143	(35,960)
Reclassification adjustment for net actuarial loss included in net income	2,335	3,527	5,564
Net actuarial loss adjustment on pension plans and other postretirement benefits	46,515	12,670	(30,396)
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	142	98	60
Prior service cost adjustment on pension plans and other postretirement benefits	142	(3,440)	60
Reclassification adjustment for loss on cash flow hedge included in net income		151	190
Total other comprehensive income (loss), net of tax	34,840	2,571	(33,500)
Comprehensive income	$ 101,433	$ 55,662	$ 33,709