Other Comprehensive Income (Components of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, before tax	$ (1,912)	$ 5,951	$ 14,238	$ 3,457
Total other comprehensive income (loss), tax effect	768	(2,390)	(5,718)	(1,388)
Total other comprehensive (loss) income	(1,144)	3,561	8,520	2,069
Unrealized gains on securities available for sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (losses) gains arising during the period, before tax	(2,575)	6,146	14,260	4,111
Reclassification adjustment for losses (gains) included in net income, before tax	43	0	(54)	(645)
Total other comprehensive (loss) income, before tax	(2,532)	6,146	14,206	3,466
Net (losses) gains arising during the period, tax effect	1,034	(2,468)	(5,727)	(1,651)
Reclassification adjustment for losses (gains) included in net income, tax effect	(17)	0	22	259
Total other comprehensive income (loss), tax effect	1,017	(2,468)	(5,705)	(1,392)
Net (losses) gains arising during the period, after tax	(1,541)	3,678	8,533	2,460
Reclassification adjustment for losses (gains) included in net income, after tax	26	0	(32)	(386)
Total other comprehensive (loss) income	(1,515)	3,678	8,501	2,074
Unrealized losses on derivatives (cash flow hedges) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, before tax	384	(388)	(603)	(388)
Total other comprehensive income (loss), tax effect	(154)	156	242	156
Total other comprehensive (loss) income	230	(232)	(361)	(232)
Post-retirement obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, before tax	236	193	635	379
Total other comprehensive income (loss), tax effect	(95)	(78)	(255)	(152)
Total other comprehensive (loss) income	$ 141	$ 115	$ 380	$ 227