Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Jun. 30, 2024 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 23,103
Available-for-sale, less than 12 months, gross unrealized losses	(460)
Available-for-sale, 12 months or more, estimated fair value	2,801,246
Available-for-sale, 12 months or more, gross unrealized losses	(369,663)
Available-for-sale, total, estimated fair value	2,824,349
Available-for-sale, total, gross unrealized losses	(370,123)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	1,275
Available-for-sale, less than 12 months, gross unrealized losses	(19)
Available-for-sale, 12 months or more, estimated fair value	0
Available-for-sale, 12 months or more, gross unrealized losses	0
Available-for-sale, total, estimated fair value	1,275
Available-for-sale, total, gross unrealized losses	(19)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	989
Available-for-sale, less than 12 months, gross unrealized losses	0
Available-for-sale, 12 months or more, estimated fair value	61,692
Available-for-sale, 12 months or more, gross unrealized losses	(1,844)
Available-for-sale, total, estimated fair value	62,681
Available-for-sale, total, gross unrealized losses	(1,844)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	2,222
Available-for-sale, less than 12 months, gross unrealized losses	(174)
Available-for-sale, 12 months or more, estimated fair value	1,728,352
Available-for-sale, 12 months or more, gross unrealized losses	(200,907)
Available-for-sale, total, estimated fair value	1,730,574
Available-for-sale, total, gross unrealized losses	(201,081)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	18,617
Available-for-sale, less than 12 months, gross unrealized losses	(267)
Available-for-sale, 12 months or more, estimated fair value	835,387
Available-for-sale, 12 months or more, gross unrealized losses	(145,728)
Available-for-sale, total, estimated fair value	854,004
Available-for-sale, total, gross unrealized losses	(145,995)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	0
Available-for-sale, less than 12 months, gross unrealized losses	0
Available-for-sale, 12 months or more, estimated fair value	175,815
Available-for-sale, 12 months or more, gross unrealized losses	(21,184)
Available-for-sale, total, estimated fair value	175,815
Available-for-sale, total, gross unrealized losses	$ (21,184)