CREDIT QUALITY ASSESSMENT - Allowance for Credit or Loan Losses by Respective Loan Portfolio Segment (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 120,865	$ 136,242	$ 136,242
Provision/ (credit) for credit losses - loans	6,292	(14,491)	(13,894)
Charge-offs	(1,939)	(2,265)	(2,614)
Recoveries	645	801	1,131
Net (charge-offs)/ recoveries	(1,294)	(1,464)	(1,483)
Balance at period end	125,863	120,287	120,865
Total loans	$ 11,483,921		$ 11,366,989
Allowance for credit losses on loans to total loans ratio	1.10%		1.06%
Average loans	$ 11,384,077		$ 11,354,227
Annualized net charge-offs/ (recoveries) to average loans	0.02%		0.01%
Balance of loans individually evaluated for credit loss	$ 88,767		$ 88,168
Allowance related to loans evaluated individually	$ 23,042		$ 24,000
Individual allowance to loans evaluated individually ratio	25.96%		27.22%
Contractual balance of individually evaluated loans	$ 92,192		$ 91,105
Balance of loans collectively evaluated for credit loss	11,395,154		11,278,821
Allowance related to loans evaluated collectively	$ 102,821		$ 96,865
Collective allowance to loans evaluated collectively ratio	0.90%		0.86%
Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	$ (1)		$ 0
Total loans	4,933,329		5,104,425
Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	1,747,708		1,755,235
Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	1,184,296		988,967
Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(50)		(160)
Total loans	1,521,890		1,474,521
Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	78,027		121,419
Commercial real estate: | Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	61,439	64,737	64,737
Provision/ (credit) for credit losses - loans	2,454		(3,323)
Charge-offs	(1)		0
Recoveries	6		25
Net (charge-offs)/ recoveries	5		25
Balance at period end	63,898		61,439
Total loans	$ 4,933,329		$ 5,104,425
Allowance for credit losses on loans to total loans ratio	1.30%		1.20%
Average loans	$ 5,010,870		$ 5,133,279
Annualized net charge-offs/ (recoveries) to average loans	0.00%		0.00%
Balance of loans individually evaluated for credit loss	$ 68,782		$ 72,218
Allowance related to loans evaluated individually	$ 16,506		$ 15,353
Individual allowance to loans evaluated individually ratio	24.00%		21.26%
Contractual balance of individually evaluated loans	$ 69,948		$ 72,712
Balance of loans collectively evaluated for credit loss	4,864,547		5,032,207
Allowance related to loans evaluated collectively	$ 47,392		$ 46,086
Collective allowance to loans evaluated collectively ratio	0.97%		0.92%
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 7,536	11,646	$ 11,646
Provision/ (credit) for credit losses - loans	(713)		(4,215)
Charge-offs	0		0
Recoveries	54		105
Net (charge-offs)/ recoveries	54		105
Balance at period end	6,877		7,536
Total loans	$ 1,747,708		$ 1,755,235
Allowance for credit losses on loans to total loans ratio	0.39%		0.43%
Average loans	$ 1,740,074		$ 1,766,839
Annualized net charge-offs/ (recoveries) to average loans	(0.01%)		(0.01%)
Balance of loans individually evaluated for credit loss	$ 9,403		$ 4,640
Allowance related to loans evaluated individually	$ 1,093		$ 1,159
Individual allowance to loans evaluated individually ratio	11.62%		24.98%
Contractual balance of individually evaluated loans	$ 10,488		$ 5,623
Balance of loans collectively evaluated for credit loss	1,738,305		1,750,595
Allowance related to loans evaluated collectively	$ 5,784		$ 6,377
Collective allowance to loans evaluated collectively ratio	0.33%		0.36%
Commercial real estate: | Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 8,287	18,646	$ 18,646
Provision/ (credit) for credit losses - loans	3,843		(10,359)
Charge-offs	0		0
Recoveries	306		0
Net (charge-offs)/ recoveries	306		0
Balance at period end	12,436		8,287
Total loans	$ 1,184,296		$ 988,967
Allowance for credit losses on loans to total loans ratio	1.05%		0.84%
Average loans	$ 1,082,134		$ 1,023,669
Annualized net charge-offs/ (recoveries) to average loans	(0.06%)		0.00%
Balance of loans individually evaluated for credit loss	$ 2,127		$ 1,259
Allowance related to loans evaluated individually	$ 102		$ 102
Individual allowance to loans evaluated individually ratio	4.80%		8.10%
Contractual balance of individually evaluated loans	$ 2,152		$ 1,270
Balance of loans collectively evaluated for credit loss	1,182,169		987,708
Allowance related to loans evaluated collectively	$ 12,334		$ 8,185
Collective allowance to loans evaluated collectively ratio	1.04%		0.83%
Commercial Business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Total loans	$ 9,466,843		$ 9,353,507
Commercial Business | Commercial business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	31,932	28,027	28,027
Provision/ (credit) for credit losses - loans	(210)		4,051
Charge-offs	(1,551)		(449)
Recoveries	29		303
Net (charge-offs)/ recoveries	(1,522)		(146)
Balance at period end	30,200		31,932
Total loans	$ 1,601,510		$ 1,504,880
Allowance for credit losses on loans to total loans ratio	1.89%		2.12%
Average loans	$ 1,530,067		$ 1,440,382
Annualized net charge-offs/ (recoveries) to average loans	0.20%		0.01%
Balance of loans individually evaluated for credit loss	$ 8,455		$ 10,051
Allowance related to loans evaluated individually	$ 5,341		$ 7,386
Individual allowance to loans evaluated individually ratio	63.17%		73.49%
Contractual balance of individually evaluated loans	$ 9,604		$ 11,500
Balance of loans collectively evaluated for credit loss	1,593,055		1,494,829
Allowance related to loans evaluated collectively	$ 24,859		$ 24,546
Collective allowance to loans evaluated collectively ratio	1.56%		1.64%
Residential real estate: | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 8,890	9,424	$ 9,424
Provision/ (credit) for credit losses - loans	631		(488)
Charge-offs	(50)		(160)
Recoveries	17		114
Net (charge-offs)/ recoveries	(33)		(46)
Balance at period end	9,488		8,890
Total loans	$ 1,521,890		$ 1,474,521
Allowance for credit losses on loans to total loans ratio	0.62%		0.60%
Average loans	$ 1,505,013		$ 1,380,496
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	1,521,890		1,474,521
Allowance related to loans evaluated collectively	$ 9,488		$ 8,890
Collective allowance to loans evaluated collectively ratio	0.62%		0.60%
Residential real estate: | Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 729	1,337	$ 1,337
Provision/ (credit) for credit losses - loans	(367)		(608)
Charge-offs	0		0
Recoveries	0		0
Net (charge-offs)/ recoveries	0		0
Balance at period end	362		729
Total loans	$ 78,027		$ 121,419
Allowance for credit losses on loans to total loans ratio	0.46%		0.60%
Average loans	$ 98,547		$ 187,599
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	78,027		121,419
Allowance related to loans evaluated collectively	$ 362		$ 729
Collective allowance to loans evaluated collectively ratio	0.46%		0.60%
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 2,052	$ 2,425	$ 2,425
Provision/ (credit) for credit losses - loans	654		1,048
Charge-offs	(337)		(2,005)
Recoveries	233		584
Net (charge-offs)/ recoveries	(104)		(1,421)
Balance at period end	2,602		2,052
Total loans	$ 417,161		$ 417,542
Allowance for credit losses on loans to total loans ratio	0.62%		0.49%
Average loans	$ 417,372		$ 421,963
Annualized net charge-offs/ (recoveries) to average loans	0.05%		0.34%
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	417,161		417,542
Allowance related to loans evaluated collectively	$ 2,602		$ 2,052
Collective allowance to loans evaluated collectively ratio	0.62%		0.49%