Securities - Securities Available-for-Sale (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,891,435,000	$ 2,094,826,000
Gross Unrealized Gains	10,000	695,000
Gross Unrealized Losses	(414,489,000)	(333,852,000)
Allowance for Credit Losses	0	0
Fair Value	1,476,956,000	1,761,669,000
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	64,097,000
Gross Unrealized Gains	0	22,000
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair Value	0	64,119,000
Obligations of State and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	892,171,000	939,193,000
Gross Unrealized Gains	10,000	673,000
Gross Unrealized Losses	(212,994,000)	(162,014,000)
Allowance for Credit Losses	0	0
Fair Value	679,187,000	777,852,000
MBS/CMO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	775,708,000	846,519,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(155,145,000)	(131,838,000)
Allowance for Credit Losses	0	0
Fair Value	620,563,000	714,681,000
US Gov’t Sponsored Entities & Agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	223,556,000	245,017,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(46,350,000)	(40,000,000)
Allowance for Credit Losses	0	0
Fair Value	$ 177,206,000	$ 205,017,000