SECURITIES - Securities Available for Sale (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Amortized cost and estimated fair value of debt securities available-for-sale
Amortized Cost	$ 714,839,000		$ 729,198,000
Unrealized Gains	149,000		157,000
Unrealized Losses	88,933,000		96,766,000
Allowance for credit losses	0
Estimated Fair Value	626,055,000		632,589,000
Amortized Cost
Within one year	3,141,000
After one, but within five years	104,669,000
After five, but within ten years	18,883,000
After ten years	471,000
Total	127,164,000
Total	714,839,000		729,198,000
Fair Value
Within one year	3,102,000
After one, but within five years	98,309,000
After five, but within ten years	14,501,000
After ten years	460,000
Total	116,372,000
Total	626,055,000		632,589,000
Proceeds from sales and calls of securities resulting in gains or losses
Debt securities, gain (loss)	0	$ 0
U.S. Treasury notes and bonds
Amortized cost and estimated fair value of debt securities available-for-sale
Amortized Cost	61,619,000		61,800,000
Unrealized Gains	0		0
Unrealized Losses	5,291,000		6,225,000
Allowance for credit losses	0
Estimated Fair Value	56,328,000		55,574,000
Amortized Cost
Total	61,619,000		61,800,000
Fair Value
Total	56,328,000		55,574,000
Mortgage-backed securities, residential
Amortized cost and estimated fair value of debt securities available-for-sale
Amortized Cost	508,906,000		518,838,000
Unrealized Gains	0		0
Unrealized Losses	76,252,000		83,707,000
Allowance for credit losses	0
Estimated Fair Value	432,654,000		435,131,000
Amortized Cost
Without single maturity date	508,906,000
Total	508,906,000		518,838,000
Fair Value
Without single maturity date	432,654,000
Total	432,654,000		435,131,000
Obligations of states and political subdivisions
Amortized cost and estimated fair value of debt securities available-for-sale
Amortized Cost	39,795,000		39,828,000
Unrealized Gains	19,000		2,000
Unrealized Losses	400,000		938,000
Allowance for credit losses	0
Estimated Fair Value	39,414,000		38,892,000
Amortized Cost
Total	39,795,000		39,828,000
Fair Value
Total	39,414,000		38,892,000
Corporate bonds and notes
Amortized cost and estimated fair value of debt securities available-for-sale
Amortized Cost	25,750,000		25,750,000
Unrealized Gains	0		0
Unrealized Losses	5,120,000		3,780,000
Allowance for credit losses	0
Estimated Fair Value	20,630,000		21,970,000
Amortized Cost
Total	25,750,000		25,750,000
Fair Value
Total	20,630,000		21,970,000
SBA loan pools
Amortized cost and estimated fair value of debt securities available-for-sale
Amortized Cost	78,769,000		82,982,000
Unrealized Gains	130,000		155,000
Unrealized Losses	1,870,000		2,116,000
Allowance for credit losses	0
Estimated Fair Value	77,029,000		81,022,000
Amortized Cost
Without single maturity date	78,769,000
Total	78,769,000		82,982,000
Fair Value
Without single maturity date	77,029,000
Total	$ 77,029,000		$ 81,022,000