Other Comprehensive Income - Components of Other Comprehensive Income and Related Tax Effects (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Unrealized holding (losses) gains on available for sale securities	$ (1,838)	$ (623)	$ 16,141
Less reclassification adjustment for gains recognized in earnings	(1,005)	(666)	(429)
Net unrealized (losses) gains	(1,921)	(1,289)	15,712
Tax effect	672	452	(5,498)
Net-of-tax amount	(1,249)	(837)	10,214
Unrealized holding gains (losses) on available for sale securities for which a portion of an other-than-temporary impairment has been recognized in earnings	(442)	2,508	244
Less reclassification adjustment for gains recognized in earnings	(922)	0	0
Net unrealized gains (losses)	(1,364)	2,508	244
Tax effect	477	(878)	(86)
Net-of-tax amount	(887)	1,630	158
Actuarial loss on postemployment health care plan	(282)	(311)	(117)
Net amortization of transition obligation and actuarial gain	184	173	149
Net unrealized loss on postemployment health care plan	(98)	(138)	32
Tax effect	34	48	(11)
Net-of-tax amount	(64)	(90)	21
Unrealized loss on interest rate swap	(63)	(168)	(213)
Less reclassification adjustment for losses recognized in earnings	340	378	384
Net unrealized gain	277	210	171
Tax effect	(97)	(73)	(60)
Net-of-tax amount	180	137	111
Total other comprehensive (loss) income	$ (2,020)	$ 840	$ 10,504