Comprehensive Income - Components of Other Comprehensive Income and Related Tax Effects (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Equity [Abstract]
Unrealized holding gains (losses) on available for sale securities before reclassifications	$ (686)	$ 144	$ (133)	$ (3,498)
Amounts reclassified out of accumulated other comprehensive income
Unrealized holding gains (losses) on available for sale securities after reclassifications	(686)	144	(133)	(3,498)
Tax effect	288	(61)	56	1,471
Unrealized holding gains (losses) on available for sale securities, net of tax	(398)	83	(77)	(2,027)
Change in unfunded status of the supplemental retirement plans before reclassifications
Amounts reclassified out of accumulated other comprehensive income:
Amortization of prior service cost	5		15
Amortization of actuarial losses	4		12
Total amounts reclassified out of accumulated other comprehensive income	9		27
Change in unfunded status of the supplemental retirement plans after reclassifications	9		27
Tax effect	(3)		(11)
Change in unfunded status of the supplemental retirement plans, net of tax	6		16
Change in joint beneficiary agreement liability before reclassifications
Amounts reclassified out of accumulated other comprehensive income
Change in joint beneficiary agreement liability after reclassifications
Tax effect
Change in joint beneficiary agreement liability, net of tax
Total other comprehensive income (loss)	$ (392)	$ 83	$ (61)	$ (2,027)