CREDIT QUALITY ASSESSMENT - Allowance for Credit or Loan Losses by Respective Loan Portfolio Segment (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 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	12,602	(11,320)	(13,894)
Charge-offs	(2,810)	(2,518)	(2,614)
Recoveries	771	956	1,131
Net (charge-offs)/ recoveries	(2,039)	(1,562)	(1,483)
Balance at period end	131,428	123,360	120,865
Total loans	$ 11,491,921		$ 11,366,989
Allowance for credit losses on loans to total loans ratio	1.14%		1.06%
Average loans	$ 11,409,514		$ 11,354,227
Annualized net charge-offs/ (recoveries) to average loans	0.02%		0.01%
Balance of loans individually evaluated for credit loss	$ 121,219		$ 88,168
Allowance related to loans evaluated individually	$ 37,326		$ 24,000
Individual allowance to loans evaluated individually ratio	30.79%		27.22%
Contractual balance of individually evaluated loans	$ 125,181		$ 91,105
Balance of loans collectively evaluated for credit loss	11,370,702		11,278,821
Allowance related to loans evaluated collectively	$ 94,102		$ 96,865
Collective allowance to loans evaluated collectively ratio	0.83%		0.86%
Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	$ (401)		$ 0
Total loans	4,868,467		5,104,425
Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	1,737,327		1,755,235
Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(135)		0
Total loans	1,255,609		988,967
Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(50)		(160)
Total loans	1,529,786		1,474,521
Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	0		0
Total loans	53,639		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	(6,616)		(3,323)
Charge-offs	(401)		0
Recoveries	9		25
Net (charge-offs)/ recoveries	(392)		25
Balance at period end	54,431		61,439
Total loans	$ 4,868,467		$ 5,104,425
Allowance for credit losses on loans to total loans ratio	1.12%		1.20%
Average loans	$ 4,964,914		$ 5,133,279
Annualized net charge-offs/ (recoveries) to average loans	0.01%		0.00%
Balance of loans individually evaluated for credit loss	$ 70,720		$ 72,218
Allowance related to loans evaluated individually	$ 16,286		$ 15,353
Individual allowance to loans evaluated individually ratio	23.03%		21.26%
Contractual balance of individually evaluated loans	$ 72,313		$ 72,712
Balance of loans collectively evaluated for credit loss	4,797,747		5,032,207
Allowance related to loans evaluated collectively	$ 38,145		$ 46,086
Collective allowance to loans evaluated collectively ratio	0.80%		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	(1,296)		(4,215)
Charge-offs	0		0
Recoveries	81		105
Net (charge-offs)/ recoveries	81		105
Balance at period end	6,321		7,536
Total loans	$ 1,737,327		$ 1,755,235
Allowance for credit losses on loans to total loans ratio	0.36%		0.43%
Average loans	$ 1,740,608		$ 1,766,839
Annualized net charge-offs/ (recoveries) to average loans	(0.01%)		(0.01%)
Balance of loans individually evaluated for credit loss	$ 9,639		$ 4,640
Allowance related to loans evaluated individually	$ 1,059		$ 1,159
Individual allowance to loans evaluated individually ratio	10.99%		24.98%
Contractual balance of individually evaluated loans	$ 10,803		$ 5,623
Balance of loans collectively evaluated for credit loss	1,727,688		1,750,595
Allowance related to loans evaluated collectively	$ 5,262		$ 6,377
Collective allowance to loans evaluated collectively ratio	0.30%		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	19,008		(10,359)
Charge-offs	(135)		0
Recoveries	330		0
Net (charge-offs)/ recoveries	195		0
Balance at period end	27,490		8,287
Total loans	$ 1,255,609		$ 988,967
Allowance for credit losses on loans to total loans ratio	2.19%		0.84%
Average loans	$ 1,139,517		$ 1,023,669
Annualized net charge-offs/ (recoveries) to average loans	(0.02%)		0.00%
Balance of loans individually evaluated for credit loss	$ 31,816		$ 1,259
Allowance related to loans evaluated individually	$ 13,444		$ 102
Individual allowance to loans evaluated individually ratio	42.26%		8.10%
Contractual balance of individually evaluated loans	$ 31,829		$ 1,270
Balance of loans collectively evaluated for credit loss	1,223,793		987,708
Allowance related to loans evaluated collectively	$ 14,046		$ 8,185
Collective allowance to loans evaluated collectively ratio	1.15%		0.83%
Commercial Business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Total loans	$ 9,482,329		$ 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	805		4,051
Charge-offs	(1,803)		(449)
Recoveries	31		303
Net (charge-offs)/ recoveries	(1,772)		(146)
Balance at period end	30,965		31,932
Total loans	$ 1,620,926		$ 1,504,880
Allowance for credit losses on loans to total loans ratio	1.91%		2.12%
Average loans	$ 1,546,498		$ 1,440,382
Annualized net charge-offs/ (recoveries) to average loans	0.15%		0.01%
Balance of loans individually evaluated for credit loss	$ 9,044		$ 10,051
Allowance related to loans evaluated individually	$ 6,537		$ 7,386
Individual allowance to loans evaluated individually ratio	72.28%		73.49%
Contractual balance of individually evaluated loans	$ 10,236		$ 11,500
Balance of loans collectively evaluated for credit loss	1,611,882		1,494,829
Allowance related to loans evaluated collectively	$ 24,428		$ 24,546
Collective allowance to loans evaluated collectively ratio	1.52%		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	355		(488)
Charge-offs	(50)		(160)
Recoveries	52		114
Net (charge-offs)/ recoveries	2		(46)
Balance at period end	9,247		8,890
Total loans	$ 1,529,786		$ 1,474,521
Allowance for credit losses on loans to total loans ratio	0.60%		0.60%
Average loans	$ 1,512,209		$ 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	1,529,786		1,474,521
Allowance related to loans evaluated collectively	$ 9,247		$ 8,890
Collective allowance to loans evaluated collectively ratio	0.60%		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	(420)		(608)
Charge-offs	0		0
Recoveries	0		0
Net (charge-offs)/ recoveries	0		0
Balance at period end	309		729
Total loans	$ 53,639		$ 121,419
Allowance for credit losses on loans to total loans ratio	0.58%		0.60%
Average loans	$ 87,177		$ 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	53,639		121,419
Allowance related to loans evaluated collectively	$ 309		$ 729
Collective allowance to loans evaluated collectively ratio	0.58%		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	766		1,048
Charge-offs	(421)		(2,005)
Recoveries	268		584
Net (charge-offs)/ recoveries	(153)		(1,421)
Balance at period end	2,665		2,052
Total loans	$ 426,167		$ 417,542
Allowance for credit losses on loans to total loans ratio	0.63%		0.49%
Average loans	$ 418,591		$ 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	426,167		417,542
Allowance related to loans evaluated collectively	$ 2,665		$ 2,052
Collective allowance to loans evaluated collectively ratio	0.63%		0.49%