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LOANS, Allowance for Credit Losses (Details) $ in Thousands	3 Months Ended		12 Months Ended
LOANS, Allowance for Credit Losses (Details) $ in Thousands	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2021 USD ($)
Allowance for credit losses - loans [Roll Forward]
Beginning balance	$ 49,911	$ 49,284	$ 55,652
Charge-offs		(3,901)
Recoveries		1,302
Provision		2,422
Ending balance	55,652	49,107
Liabilities for off-balance-sheet credit exposures [Roll Forward]
Beginning balance	0
Total allowance for credit losses [Roll Forward]
Beginning balance	49,911
Provision	$ 5,594	2,422
Allowance for Credit Losses [Abstract]
Allowance for credit losses to total loans ratio	0.0081
Increase in allowance for credit losses to total loans ratio over the same quarter in prior year	300.00%
Increase in allowance for credit losses to total loans ratio over the prior year end	900.00%
Forecast [Member] \| Minimum [Member] \| COVID-19 [Member]
Allowance for Credit Losses [Abstract]
Percentage of peak unemployment			8.00%
Forecast [Member] \| Maximum [Member] \| COVID-19 [Member]
Allowance for Credit Losses [Abstract]
Percentage of peak unemployment			13.00%
ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	$ 51,268		$ 55,652
Charge-offs	(3,047)
Recoveries	1,497
Provision	5,934
Ending balance	55,652
Liabilities for off-balance-sheet credit exposures [Roll Forward]
Beginning balance	1,185		845
Charge-offs	0
Recoveries	0
Provision	(340)
Ending balance	845
Total allowance for credit losses [Roll Forward]
Beginning balance	52,453		56,497
Charge-offs	(3,047)
Recoveries	1,497
Provision	5,594
Ending balance	56,497
ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	1,357
Liabilities for off-balance-sheet credit exposures [Roll Forward]
Beginning balance	1,185
Total allowance for credit losses [Roll Forward]
Beginning balance	2,542
Purchased Credit Impaired [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	163	33
Charge-offs		0
Recoveries		0
Provision		122
Ending balance		155
Purchased Credit Impaired [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	0		0
Charge-offs	0
Recoveries	0
Provision	0
Ending balance	0
Purchased Credit Impaired [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	(163)
Purchased Credit Deteriorated [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	0
Purchased Credit Deteriorated [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	3,072		3,046
Charge-offs	0
Recoveries	0
Provision	(26)
Ending balance	3,046
Purchased Credit Deteriorated [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	3,072
Commercial Portfolio Segment [Member] \| Business Lending [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	19,426	18,522
Charge-offs		(1,216)
Recoveries		134
Provision		831
Ending balance		18,271
Commercial Portfolio Segment [Member] \| Business Lending [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	19,714		19,489
Charge-offs	(176)
Recoveries	138
Provision	(187)
Ending balance	19,489
Commercial Portfolio Segment [Member] \| Business Lending [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	288
Residential Portfolio Segment [Member] \| Consumer Mortgage [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	10,269	10,124
Charge-offs		(253)
Recoveries		22
Provision		424
Ending balance		10,317
Residential Portfolio Segment [Member] \| Consumer Mortgage [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	9,218		12,430
Charge-offs	(186)
Recoveries	8
Provision	3,390
Ending balance	12,430
Residential Portfolio Segment [Member] \| Consumer Mortgage [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	(1,051)
Consumer Portfolio Segment [Member] \| Consumer Indirect [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	13,712	14,366
Charge-offs		(1,823)
Recoveries		962
Provision		746
Ending balance		14,251
Consumer Portfolio Segment [Member] \| Consumer Indirect [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	12,715		13,694
Charge-offs	(2,079)
Recoveries	1,163
Provision	1,895
Ending balance	13,694
Consumer Portfolio Segment [Member] \| Consumer Indirect [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	(997)
Consumer Portfolio Segment [Member] \| Consumer Direct [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	3,255	3,095
Charge-offs		(535)
Recoveries		179
Provision		317
Ending balance		3,056
Consumer Portfolio Segment [Member] \| Consumer Direct [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	2,612		3,737
Charge-offs	(533)
Recoveries	182
Provision	1,476
Ending balance	3,737
Consumer Portfolio Segment [Member] \| Consumer Direct [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	(643)
Consumer Portfolio Segment [Member] \| Home Equity [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	2,129	2,144
Charge-offs		(74)
Recoveries		5
Provision		(8)
Ending balance		2,067
Consumer Portfolio Segment [Member] \| Home Equity [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	2,937		2,484
Charge-offs	(73)
Recoveries	6
Provision	(386)
Ending balance	2,484
Consumer Portfolio Segment [Member] \| Home Equity [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	808
Unallocated Financing Receivables [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	957	1,000
Charge-offs		0
Recoveries		0
Provision		(10)
Ending balance		$ 990
Unallocated Financing Receivables [Member] \| ASU 2016-13 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	1,000		$ 772
Charge-offs	0
Recoveries	0
Provision	(228)
Ending balance	772
Unallocated Financing Receivables [Member] \| ASU 2016-13 [Member] \| Impact of ASC 326 [Member]
Allowance for credit losses - loans [Roll Forward]
Beginning balance	$ 43