Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains and losses on available for sale securities, Before tax amount	$ 2,456	$ 758	$ 3,086	$ 916
Unrealized gains and losses on available for sale securities, Tax (expense) benefit	765	174	718	236
Amortization of prior service cost included in net periodic pension cost, Before tax amount	22	(1)	66	11
Direct Cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service cost included in net periodic pension cost, Before tax amount	7	8	23	24
Amortization of prior service cost included in net periodic pension cost, Tax (expense)benefit	(6)	(2)	5	(5)
Amortization of prior service cost included in net periodic pension cost, Net of tax	1	6	28	19
Other Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains and losses on available for sale securities, Before tax amount	(199)	(213)	(1,029)	(159)
Unrealized gains and losses on available for sale securities, Tax (expense) benefit	63	70	321	193
Unrealized gains and losses on available for sale securities, Net of tax	$ (136)	$ (143)	$ (708)	$ 34