Other Comprehensive Income - Schedule of Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassification, net of tax	$ (28,209)	$ (1,296)	$ (3,039)
Reclassification, net of tax	5,324	5,311	6,641
Net change before tax	(32,185)	7,611	6,557
Net change, tax	9,300	(3,596)	(2,955)
Other comprehensive (loss) income, net	(22,885)	4,015	3,602
Unrealized Gains and Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassification, before tax	(32,123)	636	(7,294)
Before reclassification, tax	9,191	(284)	3,001
Before reclassification, net of tax	(22,932)	352	(4,293)
Reclassification adjustment before tax	2,342	20	(777)
Reclassification, tax	(485)	(9)	312
Reclassification, net of tax	1,857	11	(465)
Net change before tax	(29,781)	656	(8,071)
Net change, tax	8,706	(293)	3,313
Other comprehensive (loss) income, net	(21,075)	363	(4,758)
Non-credit Impairment Losses on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassification, before tax	0	849	719
Before reclassification, tax	0	(351)	(302)
Before reclassification, net of tax	0	498	417
Reclassification adjustment before tax	531	(284)	(921)
Reclassification, tax	(151)	117	382
Reclassification, net of tax	380	(167)	(539)
Net change before tax	531	565	(202)
Net change, tax	(151)	(234)	80
Other comprehensive (loss) income, net	380	331	(122)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassification, before tax	2,651	1,005	(4,035)
Before reclassification, tax	(777)	(429)	1,574
Before reclassification, net of tax	1,874	576	(2,461)
Reclassification adjustment before tax	3,493	8,579	13,034
Reclassification, tax	(999)	(3,551)	(5,393)
Reclassification, net of tax	2,494	5,028	7,641
Net change before tax	6,144	9,584	8,999
Net change, tax	(1,776)	(3,980)	(3,819)
Other comprehensive (loss) income, net	4,368	5,604	5,180
Net (losses) gains arising during the period
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassification, before tax	9,916	3,843	(5,837)
Before reclassification, tax	(2,765)	(1,121)	2,539
Before reclassification, net of tax	7,151	2,722	(3,298)
Amortization of prior service credit (cost )
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment before tax	(212)	(268)	300
Reclassification, tax	66	77	(119)
Reclassification, net of tax	(146)	(191)	181
Amortization of net loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment before tax	625	381	294
Reclassification, tax	(178)	(133)	(109)
Reclassification, net of tax	447	248	185
Net change
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassification, net of tax	(7,151)	(2,722)	3,298
Reclassification, net of tax	593	439	4
Net change before tax	(9,079)	(3,194)	5,831
Net change, tax	2,521	911	(2,529)
Other comprehensive (loss) income, net	$ (6,558)	$ (2,283)	$ 3,302