Investment Securities - Available-for-Sale and Held-to-Maturity Investment Securities with Unrealized Losses by Aggregated Major Security Type and Length of Time in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	$ 685,498	$ 224,979
Available-for-Sale, Less than 12 months, Unrealized Losses	(5,756)	(1,476)
Available-for-Sale, 12 months or longer, Fair Value	5,581,695	5,742,885
Available-for-Sale, 12 months or longer, Unrealized Losses	(911,283)	(872,667)
Available-for-Sale, Fair Value	6,267,193	5,967,864
Available-for-Sale, Unrealized Losses	(917,039)	(874,143)
U.S. Treasury
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	13,882	8,937
Available-for-Sale, Less than 12 months, Unrealized Losses	(77)	(42)
Available-for-Sale, 12 months or longer, Fair Value	183,031	191,027
Available-for-Sale, 12 months or longer, Unrealized Losses	(9,879)	(11,899)
Available-for-Sale, Fair Value	196,913	199,964
Available-for-Sale, Unrealized Losses	(9,956)	(11,941)
U.S. government-sponsored entities and agencies
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	3,983	0
Available-for-Sale, Less than 12 months, Unrealized Losses	(74)	0
Available-for-Sale, 12 months or longer, Fair Value	1,179,036	1,189,314
Available-for-Sale, 12 months or longer, Unrealized Losses	(184,867)	(192,717)
Available-for-Sale, Fair Value	1,183,019	1,189,314
Available-for-Sale, Unrealized Losses	(184,941)	(192,717)
Mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	498,441	90,145
Available-for-Sale, Less than 12 months, Unrealized Losses	(4,781)	(710)
Available-for-Sale, 12 months or longer, Fair Value	3,710,045	3,835,552
Available-for-Sale, 12 months or longer, Unrealized Losses	(670,311)	(621,142)
Available-for-Sale, Fair Value	4,208,486	3,925,697
Available-for-Sale, Unrealized Losses	(675,092)	(621,852)
States and political subdivisions
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	132,681	86,865
Available-for-Sale, Less than 12 months, Unrealized Losses	(691)	(495)
Available-for-Sale, 12 months or longer, Fair Value	282,382	259,767
Available-for-Sale, 12 months or longer, Unrealized Losses	(23,489)	(22,562)
Available-for-Sale, Fair Value	415,063	346,632
Available-for-Sale, Unrealized Losses	(24,180)	(23,057)
Pooled trust preferred securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	0	0
Available-for-Sale, Less than 12 months, Unrealized Losses	0	0
Available-for-Sale, 12 months or longer, Fair Value	11,274	11,337
Available-for-Sale, 12 months or longer, Unrealized Losses	(2,526)	(2,460)
Available-for-Sale, Fair Value	11,274	11,337
Available-for-Sale, Unrealized Losses	(2,526)	(2,460)
Other securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	36,511	39,032
Available-for-Sale, Less than 12 months, Unrealized Losses	(133)	(229)
Available-for-Sale, 12 months or longer, Fair Value	215,927	255,888
Available-for-Sale, 12 months or longer, Unrealized Losses	(20,211)	(21,887)
Available-for-Sale, Fair Value	252,438	294,920
Available-for-Sale, Unrealized Losses	$ (20,344)	$ (22,116)