Comprehensive Income - Components of Other Comprehensive Income and Related Tax Effects (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Equity [Abstract]
Unrealized holding gains (losses) on available for sale securities before reclassifications	$ 15	$ (105)
Amounts reclassified out of accumulated other comprehensive income-	0	0
Unrealized holding gains (losses) on available for sale securities after reclassifications	15	(105)
Tax effect	(6)	45
Unrealized holding gains (losses) on available for sale securities, net of tax	9	(60)
Change in unfunded status of the supplemental retirement plans before reclassifications	0	0
Amounts reclassified out of accumulated other comprehensive income:
Amortization of prior service cost	(14)	5
Amortization of actuarial losses	206	4
Total amounts reclassified out of accumulated other comprehensive income	192	9
Change in unfunded status of the supplemental retirement plans after reclassifications	192	9
Tax effect	(81)	(4)
Change in unfunded status of the supplemental retirement plans, net of tax	111	5
Change in joint beneficiary agreement liability before reclassifications	0	0
Amounts reclassified out of accumulated other comprehensive income	0	0
Change in joint beneficiary agreement liability after reclassifications	0	0
Tax effect	0	0
Change in joint beneficiary agreement liability, net of tax	0	0
Total other comprehensive gain (loss)	$ 120	$ (55)