Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Other comprehensive income, net of tax
Unrealized net holding gains (losses) arising during the year, pre-tax amounts	$ 12,757	$ (6,660)	$ 7,438
Reclassification adjustment for net gains related to securities available for sale included in net income, pre-tax amounts	150	3,274	144
Amortization of prior service cost and actuarial gains, pre-tax amounts	1,665	1,767	2,581
(Decrease) increase in unrecognized actuarial loss, pre-tax amounts	$ (15,546)	$ (2,595)	$ 5,637