Net Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 13,248	$ (2,620)
Period change, net of tax	1,856	7,663	3,185	15,767
Ending Balance	16,433	13,147	16,433	13,147
Unrealized Gain(Loss) on Investements Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			20,006	3,764
Period change, net of tax			2,646	15,232
Ending Balance	22,652	18,996	22,652	18,996
Pension Plans, Defined Benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(6,758)	(6,384)
Period change, net of tax			539	535
Ending Balance	$ (6,219)	$ (5,849)	$ (6,219)	$ (5,849)