CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 53,091	$ 67,209	$ 73,734
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)	60	95
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)
Comprehensive income	$ 55,662	$ 33,709	$ 61,352