Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Jun. 30, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 91,580
Available-for-sale, less than 12 months, gross unrealized losses	(7,841)
Available-for-sale, 12 months or more, estimated fair value	3,440,690
Available-for-sale, 12 months or more, gross unrealized losses	(420,113)
Available-for-sale, total, estimated fair value	3,532,270
Available-for-sale, total, gross unrealized losses	(427,954)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	776
Available-for-sale, less than 12 months, gross unrealized losses	(21)
Available-for-sale, 12 months or more, estimated fair value	1,433
Available-for-sale, 12 months or more, gross unrealized losses	(41)
Available-for-sale, total, estimated fair value	2,209
Available-for-sale, total, gross unrealized losses	(62)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	22,246
Available-for-sale, less than 12 months, gross unrealized losses	(95)
Available-for-sale, 12 months or more, estimated fair value	149,445
Available-for-sale, 12 months or more, gross unrealized losses	(7,127)
Available-for-sale, total, estimated fair value	171,691
Available-for-sale, total, gross unrealized losses	(7,222)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	2,707
Available-for-sale, less than 12 months, gross unrealized losses	(85)
Available-for-sale, 12 months or more, estimated fair value	2,270,299
Available-for-sale, 12 months or more, gross unrealized losses	(249,825)
Available-for-sale, total, estimated fair value	2,273,006
Available-for-sale, total, gross unrealized losses	(249,910)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	17,045
Available-for-sale, less than 12 months, gross unrealized losses	(379)
Available-for-sale, 12 months or more, estimated fair value	846,298
Available-for-sale, 12 months or more, gross unrealized losses	(143,464)
Available-for-sale, total, estimated fair value	863,343
Available-for-sale, total, gross unrealized losses	(143,843)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	48,806
Available-for-sale, less than 12 months, gross unrealized losses	(7,261)
Available-for-sale, 12 months or more, estimated fair value	173,215
Available-for-sale, 12 months or more, gross unrealized losses	(19,656)
Available-for-sale, total, estimated fair value	222,021
Available-for-sale, total, gross unrealized losses	$ (26,917)