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	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	$ 6,315,610	$ 3,775,098
Available-for-Sale, Less than 12 Months, Unrealized Losses	(286,288)	(90,987)
Available-for-Sale, 12 months or longer, Fair Value	1,388,842	509,992
Available-for-Sale, 12 months or longer, Unrealized Losses	(181,629)	(27,248)
Available-for-Sale, Fair Value	7,704,452	4,285,090
Available-for-Sale, Unrealized Losses	(467,917)	(118,235)
U.S. Treasury
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	419,024	91,063
Available-for-Sale, Less than 12 Months, Unrealized Losses	(8,887)	(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	419,024	91,063
Available-for-Sale, Unrealized Losses	(8,887)	(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	987,337	1,032,566
Available-for-Sale, Less than 12 Months, Unrealized Losses	(73,226)	(21,167)
Available-for-Sale, 12 months or longer, Fair Value	531,640	312,949
Available-for-Sale, 12 months or longer, Unrealized Losses	(77,027)	(15,847)
Available-for-Sale, Fair Value	1,518,977	1,345,515
Available-for-Sale, Unrealized Losses	(150,253)	(37,014)
Mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	4,355,133	2,415,923
Available-for-Sale, Less than 12 Months, Unrealized Losses	(184,282)	(59,277)
Available-for-Sale, 12 months or longer, Fair Value	823,217	163,685
Available-for-Sale, 12 months or longer, Unrealized Losses	(99,177)	(6,797)
Available-for-Sale, Fair Value	5,178,350	2,579,608
Available-for-Sale, Unrealized Losses	(283,459)	(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	276,808	178,570
Available-for-Sale, Less than 12 Months, Unrealized Losses	(9,885)	(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	276,808	181,299
Available-for-Sale, Unrealized Losses	(9,885)	(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	9,664	9,496
Available-for-Sale, 12 months or longer, Unrealized Losses	(4,097)	(4,260)
Available-for-Sale, Fair Value	9,664	9,496
Available-for-Sale, Unrealized Losses	(4,097)	(4,260)
Other securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	277,308	56,976
Available-for-Sale, Less than 12 Months, Unrealized Losses	(10,008)	(943)
Available-for-Sale, 12 months or longer, Fair Value	24,321	21,133
Available-for-Sale, 12 months or longer, Unrealized Losses	(1,328)	(311)
Available-for-Sale, Fair Value	301,629	78,109
Available-for-Sale, Unrealized Losses	$ (11,336)	$ (1,254)