Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 3,363,288	$ 3,431,679
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	153	16,041
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	410,663	152,289
Debt Securities, Held-to-maturity, Fair Value	2,952,778	3,295,431
Securities, held-to-maturity, allowance for credit loss	(500)	(500)
Securities held to maturity, net of allowance for credit losses of $500 at both September 30, 2026 and December 31, 2025	3,362,788	3,431,179
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,058,075	1,113,474
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	5,952
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	74,954	29,220
Debt Securities, Held-to-maturity, Fair Value	983,121	1,090,206
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $500 at both September 30, 2026 and December 31, 2025	1,058,075	1,113,474
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	2,303,713	2,316,705
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	153	10,089
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	335,707	123,068
Debt Securities, Held-to-maturity, Fair Value	1,968,159	2,203,726
Securities, held-to-maturity, allowance for credit loss	(500)	(500)
Securities held to maturity, net of allowance for credit losses of $500 at both September 30, 2026 and December 31, 2025	2,303,213	2,316,205
Other Investments [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	2	1
Debt Securities, Held-to-maturity, Fair Value	1,498	1,499
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $500 at both September 30, 2026 and December 31, 2025	$ 1,500	$ 1,500