Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Net unrealized loss on securities available for sale and transferred securities	$ 219,058	$ 327,184
Allowance for credit losses	69,992	67,697
Lease liabilities under operating leases	62,239	64,691
Bonus accrual	15,642	13,753
Stock-based compensation	6,623	6,321
Net actuarial loss on defined benefit post-retirement benefit plans	5,020	5,630
Deferred loan and lease origination fees	3,898	3,990
FDIC deposit insurance special assessment	1,195	8,647
Other	6,221	4,882
Total gross deferred tax assets	389,888	502,795
Right-of-use assets under operating leases	(54,427)	(56,759)
Premises and equipment	(36,614)	(38,352)
Intangible assets	(21,605)	(16,434)
Defined benefit post-retirement benefit plans	(14,149)	(13,591)
Other	(1,964)	(2,422)
Total gross deferred tax liabilities	(128,759)	(127,558)
Deferred Tax Assets, Net	$ 261,129	$ 375,237