Reclassification Adjustments Out of Accumulated Other Comprehensive Income (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
Comprehensive Income [Line Items]
Investment securities gains	$ 0	$ 296	$ 118		$ 459
Income before taxes			118		459
Tax expense			47		183
Net income			71		276
Recognized actuarial loss 1	249	197	1,176	[1]	896	[1]
Income before taxes			1,176		896
Tax expense			461		357
Net income			$ 715		$ 539

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