Other Comprehensive Income - Components of Other Comprehensive Income and Related Tax Effects (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Unrealized holding (losses) gains on available for sale securities	$ (623)	$ 16,141	$ (36,130)
Less reclassification adjustment for gains recognized in earnings	(666)	(429)	(355)
Net unrealized (losses) gains	(1,289)	15,712	(36,485)
Tax effect	452	(5,498)	12,770
Net-of-tax amount	(837)	10,214	(23,715)
Unrealized holding gains on available for sale securities for which a portion of an other-than-temporary impairment has been recognized in earnings	2,508	244	61
Less reclassification adjustment for impairment loss recognized in earnings	0	0	0
Net unrealized gains	2,508	244	61
Tax effect	(878)	(86)	(21)
Net-of-tax amount	1,630	158	40
Actuarial loss on postemployment health care plan	(311)	(117)	(219)
Net amortization of transition obligation and actuarial gain	173	149	61
Net unrealized loss on postemployment health care plan	(138)	32	(158)
Tax effect	48	(11)	55
Net-of-tax amount	(90)	21	(103)
Unrealized gain (loss) on interest rate swap	(168)	(213)	229
Less reclassification adjustment for losses recognized in earnings	378	384	400
Net unrealized gain (loss)	210	171	629
Tax effect	(73)	(60)	(220)
Net-of-tax amount	137	111	409
Other comprehensive income (loss)	$ 840	$ 10,504	$ (23,369)