CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME [Abstract]
Defined benefit plan adjustments, tax	$ 2,933	$ 1,273	$ (1,021)
Amortization and reversal of net unrealized loss on securities transferred from available-for-sale to held-to-maturity, tax	(201)	(83)	(1,625)
Non-credit component of OTTI charge recognized during the period, tax	11	127	1,356
Reduction in non-credit component of OTTI charge, tax	(585)	(1,130)	(391)
Reclassification adjustment for securities sold during the period, tax	(10)	384	195
Net unrealized securities gains arising during the period, tax	$ 615	$ 474	$ (4,604)