Other Comprehensive Income (Components of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, before tax	$ 11,221	$ 6,193
Total other comprehensive (loss) income, tax effect	(4,506)	(2,487)
Current - period other comprehensive income	6,715	3,706
Unrealized gains on securities available for sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (losses) gains, before tax	11,856	6,202
Reclassification adjustment, before tax	(96)	(2)
Income tax expense	39	1
Total other comprehensive (loss) income, before tax	11,760	6,200
Net (losses) gains, tax effect	(4,762)	(2,491)
Total other comprehensive (loss) income, tax effect	(4,723)	(2,490)
Net (losses) gains, after tax	7,094	3,711
Reclassification adjustment, after tax	(57)	(1)
Current - period other comprehensive income	7,037	3,710
Unrealized losses on derivatives (cash flow hedges) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, before tax	(704)	0
Total other comprehensive (loss) income, tax effect	(283)	0
Current - period other comprehensive income	(421)	0
Post-retirement obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive (loss) income, before tax	165	(7)
Total other comprehensive (loss) income, tax effect	(66)	3
Current - period other comprehensive income	$ 99	$ (4)