CREDIT QUALITY ASSESSMENT - Allowance for Credit or Loan Losses by Respective Loan Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 136,242	$ 109,145	$ 109,145
Provision/ (credit) for credit losses - loans	(18,945)	1,635	26,680
Charge-offs	(171)	(306)	(1,105)
Recoveries	487	114	1,522
Net recoveries (charge-offs)	316	(192)	417
Balance at period end	117,613	110,588	136,242
Total loans	$ 11,395,241		$ 11,396,706
Allowance for credit losses on loans to total loans ratio	1.03%		1.20%
Average loans	$ 11,388,459		$ 10,638,882
Annualized net charge-offs/ (recoveries) to average loans	(0.01%)		0.00%
Balance of loans individually evaluated for credit loss	$ 29,842		$ 26,197
Allowance related to loans evaluated individually	$ 9,870		$ 6,902
Individual allowance to loans evaluated individually ratio	33.07%		26.35%
Contractual balance of individually evaluated loans	$ 31,937		$ 29,475
Balance of loans collectively evaluated for credit loss	11,365,399		11,370,509
Allowance related to loans evaluated collectively	$ 107,743		$ 129,340
Collective allowance to loans evaluated collectively ratio	0.95%		1.14%
Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	$ 0		$ 0
Total loans	5,167,456		5,130,094
Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	1,769,928		1,775,037
Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	1,046,665		1,090,028
Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(23)		(155)
Total loans	1,328,524		1,287,933
Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	223,456		224,772
Commercial real estate: | Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	64,737	45,289	45,289
Provision/ (credit) for credit losses - loans	(7,780)		19,128
Charge-offs	0		0
Recoveries	5		320
Net recoveries (charge-offs)	5		320
Balance at period end	56,962		64,737
Total loans	$ 5,167,456		$ 5,130,094
Allowance for credit losses on loans to total loans ratio	1.10%		1.26%
Average loans	$ 5,136,204		$ 4,681,607
Annualized net charge-offs/ (recoveries) to average loans	0.00%		(0.01%)
Balance of loans individually evaluated for credit loss	$ 15,451		$ 9,943
Allowance related to loans evaluated individually	$ 1,935		$ 134
Individual allowance to loans evaluated individually ratio	12.52%		1.35%
Contractual balance of individually evaluated loans	$ 15,526		$ 10,882
Balance of loans collectively evaluated for credit loss	5,152,005		5,120,151
Allowance related to loans evaluated collectively	$ 55,027		$ 64,603
Collective allowance to loans evaluated collectively ratio	1.07%		1.26%
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 11,646	11,687	$ 11,687
Provision/ (credit) for credit losses - loans	(1,796)		(90)
Charge-offs	0		0
Recoveries	26		49
Net recoveries (charge-offs)	26		49
Balance at period end	9,876		11,646
Total loans	$ 1,769,928		$ 1,775,037
Allowance for credit losses on loans to total loans ratio	0.56%		0.66%
Average loans	$ 1,769,680		$ 1,730,293
Annualized net charge-offs/ (recoveries) to average loans	(0.01%)		0.00%
Balance of loans individually evaluated for credit loss	$ 4,949		$ 6,155
Allowance related to loans evaluated individually	$ 1,259		$ 1,261
Individual allowance to loans evaluated individually ratio	25.44%		20.49%
Contractual balance of individually evaluated loans	$ 5,694		$ 6,849
Balance of loans collectively evaluated for credit loss	1,764,979		1,768,882
Allowance related to loans evaluated collectively	$ 8,617		$ 10,385
Collective allowance to loans evaluated collectively ratio	0.49%		0.59%
Commercial real estate: | Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 18,646	20,322	$ 20,322
Provision/ (credit) for credit losses - loans	(6,693)		(1,676)
Charge-offs	0		0
Recoveries	0		0
Net recoveries (charge-offs)	0		0
Balance at period end	11,953		18,646
Total loans	$ 1,046,665		$ 1,090,028
Allowance for credit losses on loans to total loans ratio	1.14%		1.71%
Average loans	$ 1,082,791		$ 1,112,936
Annualized net charge-offs/ (recoveries) to average loans	0.00%		0.00%
Balance of loans individually evaluated for credit loss	$ 0		$ 0
Allowance related to loans evaluated individually	$ 0		$ 0
Individual allowance to loans evaluated individually ratio	0.00%		0.00%
Contractual balance of individually evaluated loans	$ 0		$ 0
Balance of loans collectively evaluated for credit loss	1,046,665		1,090,028
Allowance related to loans evaluated collectively	$ 11,953		$ 18,646
Collective allowance to loans evaluated collectively ratio	1.14%		1.71%
Commercial Business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Total loans	$ 9,421,527		$ 9,451,044
Contractual balance of individually evaluated loans	10,717		9,893
Commercial Business | Commercial business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	28,027	23,170	23,170
Provision/ (credit) for credit losses - loans	(2,254)		4,774
Charge-offs	(54)		(716)
Recoveries	181		799
Net recoveries (charge-offs)	127		83
Balance at period end	25,900		28,027
Total loans	$ 1,437,478		$ 1,455,885
Allowance for credit losses on loans to total loans ratio	1.80%		1.93%
Average loans	$ 1,444,588		$ 1,351,906
Annualized net charge-offs/ (recoveries) to average loans	(0.04%)		(0.01%)
Balance of loans individually evaluated for credit loss	$ 9,442		$ 8,274
Allowance related to loans evaluated individually	$ 6,676		$ 5,507
Individual allowance to loans evaluated individually ratio	70.71%		66.56%
Balance of loans collectively evaluated for credit loss	$ 1,428,036		$ 1,447,611
Allowance related to loans evaluated collectively	$ 19,224		$ 22,520
Collective allowance to loans evaluated collectively ratio	1.35%		1.56%
Residential real estate: | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 9,424	5,384	$ 5,384
Provision/ (credit) for credit losses - loans	350		4,093
Charge-offs	(23)		(155)
Recoveries	2		102
Net recoveries (charge-offs)	(21)		(53)
Balance at period end	9,753		9,424
Total loans	$ 1,328,524		$ 1,287,933
Allowance for credit losses on loans to total loans ratio	0.73%		0.73%
Average loans	$ 1,307,761		$ 1,117,053
Annualized net charge-offs/ (recoveries) to average loans	0.01%		0.00%
Balance of loans individually evaluated for credit loss	$ 0		$ 1,487
Allowance related to loans evaluated individually	$ 0		$ 0
Individual allowance to loans evaluated individually ratio	0.00%		0.00%
Contractual balance of individually evaluated loans	$ 0		$ 1,487
Balance of loans collectively evaluated for credit loss	1,328,524		1,286,446
Allowance related to loans evaluated collectively	$ 9,753		$ 9,424
Collective allowance to loans evaluated collectively ratio	0.73%		0.73%
Residential real estate: | Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 1,337	1,048	$ 1,048
Provision/ (credit) for credit losses - loans	(233)		281
Charge-offs	0		0
Recoveries	0		8
Net recoveries (charge-offs)	0		8
Balance at period end	1,104		1,337
Total loans	$ 223,456		$ 224,772
Allowance for credit losses on loans to total loans ratio	0.49%		0.59%
Average loans	$ 223,313		$ 221,341
Annualized net charge-offs/ (recoveries) to average loans	0.00%		0.00%
Balance of loans individually evaluated for credit loss	$ 0		$ 0
Allowance related to loans evaluated individually	$ 0		$ 0
Individual allowance to loans evaluated individually ratio	0.00%		0.00%
Contractual balance of individually evaluated loans	$ 0		$ 0
Balance of loans collectively evaluated for credit loss	223,456		224,772
Allowance related to loans evaluated collectively	$ 1,104		$ 1,337
Collective allowance to loans evaluated collectively ratio	0.49%		0.59%
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 2,425	$ 2,245	$ 2,245
Provision/ (credit) for credit losses - loans	(539)		170
Charge-offs	(94)		(234)
Recoveries	273		244
Net recoveries (charge-offs)	179		10
Balance at period end	2,065		2,425
Total loans	$ 421,734		$ 432,957
Allowance for credit losses on loans to total loans ratio	0.49%		0.56%
Average loans	$ 424,122		$ 423,746
Annualized net charge-offs/ (recoveries) to average loans	(0.17%)		0.00%
Balance of loans individually evaluated for credit loss	$ 0		$ 338
Allowance related to loans evaluated individually	$ 0		$ 0
Individual allowance to loans evaluated individually ratio	0.00%		0.00%
Contractual balance of individually evaluated loans	$ 0		$ 364
Balance of loans collectively evaluated for credit loss	421,734		432,619
Allowance related to loans evaluated collectively	$ 2,065		$ 2,425
Collective allowance to loans evaluated collectively ratio	0.49%		0.56%