Net Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 13,248	$ (2,620)	$ (2,652)
Period change, net of tax	(1,936)	15,868	32
Ending Balance	11,312	13,248	(2,620)
Unrealized Gain(Loss) on Investements Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	20,006	3,764	3,845
Period change, net of tax	252	16,242	(81)
Ending Balance	20,258	20,006	3,764
Pension Plans, Defined Benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(6,758)	(6,384)	(6,497)
Period change, net of tax	(2,188)	(374)	113
Ending Balance	$ (8,946)	$ (6,758)	$ (6,384)