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, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	$ 1,032,998	$ 4,465,728
Available-for-sale, less than 12 months, unrealized losses	(32,062)	(480,166)
Available-for-sale, 12 months or longer, fair value	5,319,655	1,992,246
Available-for-sale, 12 months or longer, unrealized losses	(785,534)	(367,308)
Available-for-sale, fair value	6,352,653	6,457,974
Available-for-sale, unrealized losses	(817,596)	(847,474)
U.S. Treasury
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	23,229	130,967
Available-for-sale, less than 12 months, unrealized losses	(106)	(3,264)
Available-for-sale, 12 months or longer, fair value	190,653	66,992
Available-for-sale, 12 months or longer, unrealized losses	(10,649)	(1,925)
Available-for-sale, fair value	213,882	197,959
Available-for-sale, unrealized losses	(10,755)	(5,189)
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	96,117	454,854
Available-for-sale, less than 12 months, unrealized losses	(2,554)	(75,795)
Available-for-sale, 12 months or longer, fair value	1,097,574	720,226
Available-for-sale, 12 months or longer, unrealized losses	(199,163)	(93,453)
Available-for-sale, fair value	1,193,691	1,175,080
Available-for-sale, unrealized losses	(201,717)	(169,248)
Mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	758,680	3,207,319
Available-for-sale, less than 12 months, unrealized losses	(26,422)	(358,507)
Available-for-sale, 12 months or longer, fair value	3,513,804	1,116,205
Available-for-sale, 12 months or longer, unrealized losses	(527,068)	(258,921)
Available-for-sale, fair value	4,272,484	4,323,524
Available-for-sale, unrealized losses	(553,490)	(617,428)
States and political subdivisions
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	112,958	414,813
Available-for-sale, less than 12 months, unrealized losses	(1,576)	(25,555)
Available-for-sale, 12 months or longer, fair value	233,172	2,703
Available-for-sale, 12 months or longer, unrealized losses	(20,392)	(541)
Available-for-sale, fair value	346,130	417,516
Available-for-sale, unrealized losses	(21,968)	(26,096)
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	10,849	10,811
Available-for-sale, 12 months or longer, unrealized losses	(2,938)	(2,972)
Available-for-sale, fair value	10,849	10,811
Available-for-sale, unrealized losses	(2,938)	(2,972)
Other securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	42,014	257,775
Available-for-sale, less than 12 months, unrealized losses	(1,404)	(17,045)
Available-for-sale, 12 months or longer, fair value	273,603	75,309
Available-for-sale, 12 months or longer, unrealized losses	(25,324)	(9,496)
Available-for-sale, fair value	315,617	333,084
Available-for-sale, unrealized losses	$ (26,728)	$ (26,541)