LOANS AND ALLOWANCE FOR CREDIT LOSSES - Past due (Details) - USD ($)	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025
Allowance for credit losses
Current - 29 Days Past Due	$ 909,311,000	$ 934,045,000
Total	931,620,000	946,661,000	$ 964,181,000
90 Days or Greater Past Due and Still Accruing Interest		146,000
Financial Asset, 30 to 59 Days Past Due
Allowance for credit losses
Total	1,985,000	3,652,000
Financing Receivables, 60 to 89 Days Past Due
Allowance for credit losses
Total	4,257,000	2,270,000
Financing Receivables, Equal to Greater than 90 Days Past Due
Allowance for credit losses
Total	16,067,000	6,694,000
Financial Asset, Past Due
Allowance for credit losses
Total	22,309,000	12,616,000
Real Estate
Allowance for credit losses
Current - 29 Days Past Due	817,515,000	841,545,000
Total	839,239,000	853,668,000	863,664,000
90 Days or Greater Past Due and Still Accruing Interest		146,000
Real Estate | Financial Asset, 30 to 59 Days Past Due
Allowance for credit losses
Total	1,537,000	3,193,000
Real Estate | Financing Receivables, 60 to 89 Days Past Due
Allowance for credit losses
Total	4,120,000	2,246,000
Real Estate | Financing Receivables, Equal to Greater than 90 Days Past Due
Allowance for credit losses
Total	16,067,000	6,684,000
Real Estate | Financial Asset, Past Due
Allowance for credit losses
Total	21,724,000	12,123,000
Agricultural
Allowance for credit losses
Current - 29 Days Past Due	1,093,000	984,000
Total	1,230,000	984,000	1,117,000
Agricultural | Financing Receivables, 60 to 89 Days Past Due
Allowance for credit losses
Total	137,000
Agricultural | Financial Asset, Past Due
Allowance for credit losses
Total	137,000
Commercial and Industrial
Allowance for credit losses
Current - 29 Days Past Due	65,739,000	66,557,000
Total	66,187,000	66,924,000	68,223,000
Commercial and Industrial | Financial Asset, 30 to 59 Days Past Due
Allowance for credit losses
Total	448,000	333,000
Commercial and Industrial | Financing Receivables, 60 to 89 Days Past Due
Allowance for credit losses
Total		24,000
Commercial and Industrial | Financing Receivables, Equal to Greater than 90 Days Past Due
Allowance for credit losses
Total		10,000
Commercial and Industrial | Financial Asset, Past Due
Allowance for credit losses
Total	448,000	367,000
Consumer
Allowance for credit losses
Current - 29 Days Past Due	4,881,000	4,827,000
Total	4,881,000	4,953,000	6,544,000
Consumer | Financial Asset, 30 to 59 Days Past Due
Allowance for credit losses
Total		126,000
Consumer | Financial Asset, Past Due
Allowance for credit losses
Total		126,000
State and Political Subdivisions
Allowance for credit losses
Current - 29 Days Past Due	20,083,000	20,132,000
Total	$ 20,083,000	$ 20,132,000	$ 24,633,000