Other Comprehensive Loss - Schedule of Components of OCI (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Unrealized losses on available for sale debt securities:
Net gains (losses) arising during the period	$ 24,987	$ (8,425)	$ (3,612)
Reclassification adjustment for gains included in net income	0	0	0
Total	24,987	(8,425)	(3,612)
Unrealized (losses) gains on derivatives (cash flow hedges)	(780)
Unrealized (losses) gains on derivatives (cash flow hedges)		304	633
Amortization related to post-retirement obligations	(2,176)	1,678	(1,475)
Total other comprehensive loss	22,031	(6,443)	(4,454)
Unrealized losses on available for sale debt securities:
Net gains (losses) arising during the period	(6,636)	2,296	1,449
Reclassification adjustment for gains included in net income	0	0	0
Total	(6,636)	2,296	1,449
Unrealized (losses) gains on derivatives (cash flow hedges)	201
Unrealized (losses) gains on derivatives (cash flow hedges)		(83)	(254)
Amortization related to post-retirement obligations	561	(457)	586
Total other comprehensive loss	(5,874)	1,756	1,781
Unrealized losses on available for sale debt securities:
Net gains (losses) arising during the period	18,351	(6,129)	(2,163)
Reclassification adjustment for gains included in net income	0	0	0
Total	18,351	(6,129)	(2,163)
Unrealized (losses) gains on derivatives (cash flow hedges)	(579)
Unrealized (losses) gains on derivatives (cash flow hedges)	(579)	221	379
Amortization related to post-retirement obligations	(1,615)	1,221	(889)
Total other comprehensive income (loss)	$ 16,157	$ (4,687)	$ (2,673)