Securities (Year End Securities Held to Maturity) (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 3,619,738	$ 2,639,241
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	43,066	13,048
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	130,760	184,424
Debt Securities, Held to Maturity, Estimated Fair Value	3,532,044	2,467,865
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(310)	(158)
Securities held to maturity, net of allowance for credit losses of $310 in 2023 and $158 in 2022	3,619,428	2,639,083
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,250,431	526,122
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	76	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	54,175	65,322
Debt Securities, Held to Maturity, Estimated Fair Value	1,196,332	460,800
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0
Securities held to maturity, net of allowance for credit losses of $310 in 2023 and $158 in 2022	1,250,431	526,122
States and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	2,367,807	2,111,619
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	42,990	13,048
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	76,540	119,033
Debt Securities, Held to Maturity, Estimated Fair Value	2,334,257	2,005,634
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(310)	(158)
Securities held to maturity, net of allowance for credit losses of $310 in 2023 and $158 in 2022	2,367,497	2,111,461
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	45	69
Debt Securities, Held to Maturity, Estimated Fair Value	1,455	1,431
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0
Securities held to maturity, net of allowance for credit losses of $310 in 2023 and $158 in 2022	$ 1,500	$ 1,500