Securities (Year End Securities Held to Maturity) (Detail) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 3,431,679	$ 3,534,085
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	16,041	13,954
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	152,289	187,493
Debt Securities, Held to Maturity, Estimated Fair Value	3,295,431	3,360,546
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(500)	(310)
Securities held to maturity, net of allowance for credit losses of $500 at 2025 and $310 at 2024	3,431,179	3,533,775
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,113,474	1,193,840
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	5,952	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	29,220	71,076
Debt Securities, Held to Maturity, Estimated Fair Value	1,090,206	1,122,764
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0
Securities held to maturity, net of allowance for credit losses of $500 at 2025 and $310 at 2024	1,113,474	1,193,840
States and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	2,316,705	2,338,745
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	10,089	13,954
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	123,068	116,414
Debt Securities, Held to Maturity, Estimated Fair Value	2,203,726	2,236,285
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(500)	(310)
Securities held to maturity, net of allowance for credit losses of $500 at 2025 and $310 at 2024	2,316,205	2,338,435
Other [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,500	1,500
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	1	3
Debt Securities, Held to Maturity, Estimated Fair Value	1,499	1,497
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0
Securities held to maturity, net of allowance for credit losses of $500 at 2025 and $310 at 2024	$ 1,500	$ 1,500