INCOME TAXES (Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Computed "expected" tax on net income									$ 36,538	$ 38,665	$ 30,495
Increase (decrease) resulting from:
Nontaxable interest income									(4,011)	(3,281)	(4,423)
State income taxes, net of federal tax benefit									7,930	8,509	6,976
Tax credits									(4,521)	(6,860)	(4,085)
Valuation allowance									(374)	(1,648)	23
Excess tax expense/(benefit) on stock compensation									80	(229)	(657)
Other									411	(166)	(114)
Total income tax expense	$ 9,046	$ 13,681	$ 7,417	$ 5,909	$ 5,155	$ 7,941	$ 13,584	$ 8,310	$ 36,053	$ 34,990	$ 28,215
Effective tax rates									20.70%	19.00%	19.40%