OTHER COMPREHENSIVE INCOME : OTHER COMPREHENSIVE INCOME (LOSS)-Reclassifications (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains (losses)										$ 44	$ 2	$ 59
Income tax expense										(12,127)	(11,145)	(20,622)
NET INCOME		$ 14,364	$ 12,257	$ 12,569	$ 9,682	$ 11,056	$ 11,313	$ 15,261	$ 8,953	48,872	46,583	29,131
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
NET INCOME										(1,135)	(1,083)	(698)
Unrealized Gains and Losses on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains (losses)										44	2	59
Income tax expense										(11)	0	(23)
NET INCOME										33	2	36
Retirement Plans | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Change in funded status of post retirement benefits	[1]									(1,558)	(1,447)	(1,204)
Income tax expense										390	362	470
NET INCOME										$ (1,168)	$ (1,085)	$ (734)

[1] Included in the computation of net periodic benefit cost which is included in salaries and benefits. (see Footnote 16 for additional details).