Investment Securities - Available-for-Sale Investment Securities with Unrealized Losses by Aggregated Major Security Type and Length of Time in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	$ 6,027,199	$ 3,775,098
Available-for-sale, less than 12 months, unrealized losses	(390,064)	(90,987)
Available-for-sale, 12 months or longer, fair value	990,842	509,992
Available-for-sale, 12 months or longer, unrealized losses	(189,769)	(27,248)
Available-for-sale, fair value	7,018,041	4,285,090
Available-for-sale, unrealized losses	(579,833)	(118,235)
U.S. Treasury
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	400,802	91,063
Available-for-sale, less than 12 months, unrealized losses	(7,739)	(7,751)
Available-for-sale, 12 months or longer, fair value	0	0
Available-for-sale, 12 months or longer, unrealized losses	0	0
Available-for-sale, fair value	400,802	91,063
Available-for-sale, unrealized losses	(7,739)	(7,751)
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	803,249	1,032,566
Available-for-sale, less than 12 months, unrealized losses	(27,407)	(21,167)
Available-for-sale, 12 months or longer, fair value	437,307	312,949
Available-for-sale, 12 months or longer, unrealized losses	(95,827)	(15,847)
Available-for-sale, fair value	1,240,556	1,345,515
Available-for-sale, unrealized losses	(123,234)	(37,014)
Mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	4,149,631	2,415,923
Available-for-sale, less than 12 months, unrealized losses	(311,841)	(59,277)
Available-for-sale, 12 months or longer, fair value	509,634	163,685
Available-for-sale, 12 months or longer, unrealized losses	(89,153)	(6,797)
Available-for-sale, fair value	4,659,265	2,579,608
Available-for-sale, unrealized losses	(400,994)	(66,074)
States and political subdivisions
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	372,074	178,570
Available-for-sale, less than 12 months, unrealized losses	(24,117)	(1,849)
Available-for-sale, 12 months or longer, fair value	0	2,729
Available-for-sale, 12 months or longer, unrealized losses	0	(33)
Available-for-sale, fair value	372,074	181,299
Available-for-sale, unrealized losses	(24,117)	(1,882)
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	11,102	9,496
Available-for-sale, 12 months or longer, unrealized losses	(2,667)	(4,260)
Available-for-sale, fair value	11,102	9,496
Available-for-sale, unrealized losses	(2,667)	(4,260)
Other securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 months, fair value	301,443	56,976
Available-for-sale, less than 12 months, unrealized losses	(18,960)	(943)
Available-for-sale, 12 months or longer, fair value	32,799	21,133
Available-for-sale, 12 months or longer, unrealized losses	(2,122)	(311)
Available-for-sale, fair value	334,242	78,109
Available-for-sale, unrealized losses	$ (21,082)	$ (1,254)