Other Comprehensive Income (Loss) (Components of OCI) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Unrealized gains and losses on available for sale debt securities:
Net unrealized gains (losses) arising during the period	$ 10,417	$ (13,093)
Reclassification adjustment for gains included in net income	0	0
Total	10,417	(13,093)
Unrealized (losses) gains on Derivatives (cash flow hedges)	(432)	720
Amortization related to post-retirement obligations	(16)	84
Total other comprehensive income (loss)	9,969	(12,289)
Unrealized gains and losses on available for sale debt securities:
Net unrealized gains (losses) arising during the period	(2,839)	3,454
Reclassification adjustment for gains included in net income	0	0
Total	(2,839)	3,454
Unrealized (losses) gains on Derivatives (cash flow hedges)	118	(190)
Amortization related to post-retirement obligations	4	(22)
Total other comprehensive income (loss)	(2,717)	3,242
Unrealized gains and losses on available for sale debt securities:
Net unrealized gains (losses) arising during the period	7,578	(9,639)
Reclassification adjustment for gains included in net income	0	0
Total	7,578	(9,639)
Unrealized (losses) gains on Derivatives (cash flow hedges)	(314)	530
Amortization related to post-retirement obligations	(12)	62
Total other comprehensive income (loss)	$ 7,252	$ (9,047)