Reclassification adjustments out of accumulated other comprehensive income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Comprehensive Income [Line Items]
Investment securities gains	$ 56		$ 73
Income before taxes	56		73
Tax expense	23		29
Net income	33		44
Recognized actuarial loss 1	(364)	[1]	(350)	[1]
Income before taxes	364		350
Tax expense	146		140
Net income	$ 218		$ 210

[1] This amount is included in the computation of net periodic pension cost, see Note 10