Other Comprehensive Income - Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive Income (Loss) (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
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	$ (729)	$ (383)	$ (2,306)	$ (1,274)
Net income available to common shareholders	1,900	1,277	5,790	4,267
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income available to common shareholders	(57)	(66)	(71)	(251)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains and losses on available-for-sale securities	1	80	114	138
Income tax expense		(27)	(39)	(47)
Net income available to common shareholders	1	53	75	91
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined Benefit Pension Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial losses	(89)	(180)	(222)	(518)
Income tax expense	31	61	76	176
Net income available to common shareholders	$ (58)	$ (119)	$ (146)	$ (342)