SECURITIES - Securities Available for Sale (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Amortized cost and estimated fair value of securities available for sale [Abstract]
Amortized Cost	$ 683,712,000		$ 683,712,000		$ 542,362,000
Unrealized Gains	9,490,000		9,490,000		12,654,000
Unrealized Losses	5,608,000		5,608,000		405,000
Estimated Fair Value	687,594,000		687,594,000		554,611,000
Amortized Cost
Within one year	687,000		687,000
After one, but within five years	55,036,000		55,036,000
After five, but within ten years	14,719,000		14,719,000
After ten years	470,000		470,000
Total	70,912,000		70,912,000
Amortized Cost	683,712,000		683,712,000		542,362,000
Fair Value
Within one year	691,000		691,000
After one, but within five years	56,703,000		56,703,000
After five, but within ten years	15,388,000		15,388,000
After ten years	503,000		503,000
Total	73,285,000		73,285,000
Fair value	687,594,000		687,594,000		554,611,000
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]
Proceeds form sale of securities resulting in gain (loss)	0	$ 0	0	$ 0
U.S. Treasury notes and bonds
Amortized cost and estimated fair value of securities available for sale [Abstract]
Amortized Cost	20,548,000		20,548,000
Unrealized Gains	1,000		1,000
Unrealized Losses	30,000		30,000
Estimated Fair Value	20,519,000		20,519,000
Amortized Cost
Amortized Cost	20,548,000		20,548,000
Fair Value
Fair value	20,519,000		20,519,000
Mortgage-backed securities, residential
Amortized cost and estimated fair value of securities available for sale [Abstract]
Amortized Cost	552,066,000		552,066,000		458,245,000
Unrealized Gains	6,745,000		6,745,000		9,822,000
Unrealized Losses	5,216,000		5,216,000		201,000
Estimated Fair Value	553,595,000		553,595,000		467,866,000
Amortized Cost
Without single maturity date	552,066,000		552,066,000
Amortized Cost	552,066,000		552,066,000		458,245,000
Fair Value
Without single maturity date	553,595,000		553,595,000
Fair value	553,595,000		553,595,000		467,866,000
Obligations of states and political subdivisions
Amortized cost and estimated fair value of securities available for sale [Abstract]
Amortized Cost	40,364,000		40,364,000		40,662,000
Unrealized Gains	2,308,000		2,308,000		2,743,000
Unrealized Losses	0		0		0
Estimated Fair Value	42,672,000		42,672,000		43,405,000
Amortized Cost
Amortized Cost	40,364,000		40,364,000		40,662,000
Fair Value
Fair value	42,672,000		42,672,000		43,405,000
Corporate bonds and notes
Amortized cost and estimated fair value of securities available for sale [Abstract]
Amortized Cost	10,000,000		10,000,000		9,000,000
Unrealized Gains	129,000		129,000		47,000
Unrealized Losses	35,000		35,000		12,000
Estimated Fair Value	10,094,000		10,094,000		9,035,000
Amortized Cost
Amortized Cost	10,000,000		10,000,000		9,000,000
Fair Value
Fair value	10,094,000		10,094,000		9,035,000
SBA loan pools
Amortized cost and estimated fair value of securities available for sale [Abstract]
Amortized Cost	60,734,000		60,734,000		34,455,000
Unrealized Gains	307,000		307,000		42,000
Unrealized Losses	327,000		327,000		192,000
Estimated Fair Value	60,714,000		60,714,000		34,305,000
Amortized Cost
Without single maturity date	60,734,000		60,734,000
Amortized Cost	60,734,000		60,734,000		34,455,000
Fair Value
Without single maturity date	60,714,000		60,714,000
Fair value	$ 60,714,000		$ 60,714,000		$ 34,305,000