Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Consolidated Statements of Comprehensive Income (Unaudited) [Abstract]
Net income	$ 9,168	$ 8,909
Net unrealized holding gain (loss) on securities available for sale	(2,939)	4,880
Reclassification adjustments for net gain recognized in income	(2)	(677)
Tax effect	1,173	(1,676)
Net unrealized gain (loss) on securities available for sale	(1,768)	2,527
Amortization of net actuarial loss	132	97
Amortization of prior service credit	(66)	(66)
Tax effect	(25)	(12)
Amortization of net actuarial loss and prior service credit on pension and postretirement plans, net of tax	41	19
Other comprehensive income (loss)	(1,727)	2,546
Comprehensive income	$ 7,441	$ 11,455