Securities - Securities with Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	$ 89,738	$ 1,018,313
Less than 12 Months, Unrealized Loss	(5,210)	(177,161)
12 Months or More, Fair Value	1,385,129	603,633
12 Months or More, Unrealized Loss	(409,279)	(156,691)
Total Fair Value	1,474,867	1,621,946
Total Unrealized Loss	(414,489)	(333,852)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Loss	0	0
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Loss	0	0
Total Fair Value	0	0
Total Unrealized Loss	0	0
Obligations of State and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	89,609	579,267
Less than 12 Months, Unrealized Loss	(5,201)	(117,423)
12 Months or More, Fair Value	587,496	122,992
12 Months or More, Unrealized Loss	(207,793)	(44,591)
Total Fair Value	677,105	702,259
Total Unrealized Loss	(212,994)	(162,014)
MBS/CMO
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	129	240,344
Less than 12 Months, Unrealized Loss	(9)	(20,920)
12 Months or More, Fair Value	620,427	474,327
12 Months or More, Unrealized Loss	(155,136)	(110,918)
Total Fair Value	620,556	714,671
Total Unrealized Loss	(155,145)	(131,838)
US Gov’t Sponsored Entities & Agencies
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	198,702
Less than 12 Months, Unrealized Loss	0	(38,818)
12 Months or More, Fair Value	177,206	6,314
12 Months or More, Unrealized Loss	(46,350)	(1,182)
Total Fair Value	177,206	205,016
Total Unrealized Loss	$ (46,350)	$ (40,000)