ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY - Allowance for loan losses by portfolio segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Post adoption of ASC 326
Beginning balance				$ 61,408				$ 50,652	$ 61,408	$ 50,652	$ 48,453
Provision for credit losses	$ 0	$ 1,300	$ (1,700)	1,477	$ 920	$ 1,750	$ 5,500	6,600	1,077	14,770	3,235
Loans charged-off									(5,983)	(5,253)	(1,910)
Recoveries									2,221	1,239	874
Net loans (charged-off) recovered									(3,762)	(4,014)	(1,036)
Ending balance	67,773				61,408				67,773	61,408	50,652
Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				9,050					9,050
Ending balance					9,050					9,050
Commercial and Industrial
Post adoption of ASC 326
Beginning balance				28,333					28,333
Ending balance					28,333					28,333
Commercial and Industrial | Total commercial loans
Post adoption of ASC 326
Beginning balance				28,333				25,789	28,333	25,789	22,518
Provision for credit losses									1,966	6,640	4,259
Loans charged-off									(5,575)	(4,524)	(1,447)
Recoveries									1,559	428	459
Net loans (charged-off) recovered									(4,016)	(4,096)	(988)
Ending balance	30,595				28,333				30,595	28,333	25,789
Commercial and Industrial | Total commercial loans | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				4,312					4,312
Ending balance					4,312					4,312
Commercial Real Estate and Multi-family Residential
Post adoption of ASC 326
Beginning balance				22,907					22,907
Ending balance					22,907					22,907
Commercial Real Estate and Multi-family Residential | Total commercial loans
Post adoption of ASC 326
Beginning balance				22,907				15,796	22,907	15,796	15,393
Provision for credit losses									(632)	6,868	259
Loans charged-off									(70)	(72)	(17)
Recoveries									14	315	161
Net loans (charged-off) recovered									(56)	243	144
Ending balance	26,535				22,907				26,535	22,907	15,796
Commercial Real Estate and Multi-family Residential | Total commercial loans | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				4,316					4,316
Ending balance					4,316					4,316
Agri-business and Agricultural
Post adoption of ASC 326
Beginning balance				3,043					3,043
Ending balance					3,043					3,043
Agri-business and Agricultural | Total commercial loans
Post adoption of ASC 326
Beginning balance				3,043				3,869	3,043	3,869	4,305
Provision for credit losses									611	(826)	(444)
Loans charged-off									0	0	0
Recoveries									320	0	8
Net loans (charged-off) recovered									320	0	8
Ending balance	5,034				3,043				5,034	3,043	3,869
Agri-business and Agricultural | Total commercial loans | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				1,060					1,060
Ending balance					1,060					1,060
Other Commercial
Post adoption of ASC 326
Beginning balance				416					416
Ending balance					416					416
Other Commercial | Total commercial loans
Post adoption of ASC 326
Beginning balance				416				447	416	447	368
Provision for credit losses									(211)	(31)	79
Loans charged-off									0	0	0
Recoveries									0	0	0
Net loans (charged-off) recovered									0	0	0
Ending balance	1,146				416				1,146	416	447
Other Commercial | Total commercial loans | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				941					941
Ending balance					941					941
Consumer 1-4 Family Mortgage
Post adoption of ASC 326
Beginning balance				2,619					2,619
Ending balance					2,619					2,619
Consumer 1-4 Family Mortgage | Other consumer loans
Post adoption of ASC 326
Beginning balance				2,619				2,086	2,619	2,086	2,292
Provision for credit losses									(777)	341	(219)
Loans charged-off									(51)	(141)	(110)
Recoveries									122	333	123
Net loans (charged-off) recovered									71	192	13
Ending balance	2,866				2,619				2,866	2,619	2,086
Consumer 1-4 Family Mortgage | Other consumer loans | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				953					953
Ending balance					953					953
Other Consumer
Post adoption of ASC 326
Beginning balance				951					951
Ending balance					951					951
Other Consumer | Other consumer loans
Post adoption of ASC 326
Beginning balance				951				345	951	345	283
Provision for credit losses									(72)	959	275
Loans charged-off									(287)	(516)	(336)
Recoveries									206	163	123
Net loans (charged-off) recovered									(81)	(353)	(213)
Ending balance	1,147				951				1,147	951	345
Other Consumer | Other consumer loans | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				349					349
Ending balance					349					349
Unallocated
Post adoption of ASC 326
Beginning balance				3,139				$ 2,320	3,139	2,320	3,294
Provision for credit losses									192	819	(974)
Loans charged-off									0	0	0
Recoveries									0	0	0
Net loans (charged-off) recovered									0	0	0
Ending balance	$ 450				3,139				450	3,139	$ 2,320
Unallocated | Impact of ASC 326 Adoption
Post adoption of ASC 326
Beginning balance				$ (2,881)					$ (2,881)
Ending balance					$ (2,881)					$ (2,881)