Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ (190)	$ (4,203)	$ (3,042)
Unrealized Gains (losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss), before tax amount	(248)	(6,580)	(4,555)
Amounts reclassified from accumulated other comprehensive income (loss), tax expense (benefit)	83	2,262	1,494
Amounts reclassified from accumulated other comprehensive income (loss)	(165)	(4,318)	(3,061)
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss), before tax amount	(35)	149	29
Amounts reclassified from accumulated other comprehensive income (loss), tax expense (benefit)	10	(34)	(10)
Amounts reclassified from accumulated other comprehensive income (loss)	$ (25)	$ 115	$ 19