Other Comprehensive Income - Components of Other Comprehensive Income and Related Tax Effects (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Equity [Abstract]
Unrealized holding gains (losses) on available for sale securities	$ (36,130)	$ 6,597	$ 22,457
Less reclassification adjustment for gains recognized in earnings	(355)	(1,379)	(614)
Net unrealized gains	(36,485)	5,218	21,843
Tax effect	12,770	(1,826)	(7,642)
Net-of-tax amount	(23,715)	3,392	14,201
Unrealized holding gains (losses) on available for sale securities for which a portion of an other-than-temporary impairment has been recognized in earnings	61	260	(28)
Less reclassification adjustment for impairment loss recognized in earnings	0	0	398
Net unrealized gains	61	260	370
Tax effect	(21)	(91)	(130)
Net-of-tax amount	40	169	240
Actuarial loss on postemployment health care plan	(219)	(578)	(757)
Net amortization of transition obligation and actuarial gain	61	41	11
Net unrealized loss on postemployment health care plan	(158)	(537)	(746)
Tax effect	55	188	261
Net-of-tax amount	(103)	(349)	(485)
Unrealized loss on interest rate swap	229	(465)	(1,205)
Less reclassification adjustment for losses recognized in earnings	400	390	402
Net unrealized gain (loss)	629	(75)	(803)
Tax effect	(220)	26	281
Net-of-tax amount	409	(49)	(522)
Total other comprehensive income (loss)	$ (23,369)	$ 3,163	$ 13,434