Other Comprehensive Income - Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Unrealized losses on securities available for sale:
Change in fair value of securities available for sale, Pre Tax Amount	$ (465,532)	$ (94,979)
Less: reclassification adjustments for gains included in net income, Pre-Tax Amount	(2,172)	1,164
Net change in fair value of securities available for sale, Pre Tax Amount	(463,360)	(96,143)
Unrealized gains (losses) on cash flow hedges:
Change in fair value of cash flow hedges, Pre Tax Amount	0	0
Less: net cash flow hedge losses reclassified into interest income, Pre Tax Amount	5,298	8,274
Net change in fair value of cash flow hedges, Pre Tax Amount	(5,298)	(8,274)
Defined benefit pension plans:
Change in actuarial loss, Pre Tax Amount	0	0
Less: amortization of actuarial net loss, Pre Tax Amount	(2,798)	(3,537)
Less: amortization of prior service cost, pre tax amount	2,970	2,945
Net change in other comprehensive income for defined benefit postretirement plans, Pre Tax Amount	(172)	592
Total other comprehensive income, Pre Tax Amount	(468,830)	(103,825)
Unrealized losses on securities available for sale:
Change in fair value of securities available for sale, Tax (Expense) Benefit	112,008	20,982
Less: reclassification adjustments for gains included in net income, Tax (Expense) Benefit	673	(257)
Net change in fair value of securities available for sale, Tax (Expense) Benefit	111,335	21,239
Unrealized gains (losses) on cash flow hedges:
Change in fair value of cash flow hedges, Tax (Expense) Benefit	0	0
Less: net cash flow hedge losses reclassified into interest income, Tax (Expense) Benefit	(1,489)	(2,326)
Net change in fair value of cash flow hedges, Tax (Expense) Benefit	1,489	2,326
Defined benefit pension plans:
Change in actuarial net loss, Tax (Expense) Benefit	0	0
Less: amortization of actuarial net loss, Tax (Expense) Benefit	787	994
Less: net accretion of prior service credit, Tax (Expense) Benefit	(835)	(828)
Net change in other comprehensive income for defined benefit postretirement plans, Tax (Expense) Benefit	48	(166)
Total other comprehensive income, Tax (Expense) Benefit	112,872	23,399
Unrealized losses on securities available for sale:
Change in fair value of securities available for sale, After Tax Amount	(353,524)	(73,997)
Less: reclassification adjustment for gains included in net income, After Tax Amount	(1,499)	907
Net change in fair value of securities available for sale, After Tax Amount	(352,025)	(74,904)
Unrealized gains (losses) on cash flow hedges:
Change in fair value of cash flow hedges, After Tax Amount	0	0
Less: net cash flow hedge losses reclassified into interest income, Amount After Tax	3,809	5,948
Net change in fair value of cash flow hedges, Amount After Tax	(3,809)	(5,948)
Defined benefit pension plans:
Change in actuarial net loss, After Tax Amount	0	0
Less: amortization of actuarial net loss, After Tax Amount	(2,011)	(2,543)
Less: amortization of prior service cost, After Tax Amount	2,135	2,117
Net change in other comprehensive income for defined benefit postretirement plans, Amount After Tax	(124)	426
Total other comprehensive income, After Tax Amount	(355,958)	$ (80,426)
Total realized gain, net of tax	41,200
Balance of gain after amortization, net of tax	$ 3,600		$ 7,400