ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Credit Quality Indicators (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 8,569,142	$ 9,014,677	$ 8,534,986
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	121,165	1,336,436
2020	1,058,956	535,401
2019	479,662	383,110
2018	359,604	216,287
2017	202,748	114,764
Prior	249,878	177,504
Revolving loans amortized cost basis	5,771	6,245
Revolving loans converted to term	185,688	179,556
Total Loans	2,663,472	2,949,303	2,298,372
Gross loans	2,398,535	2,700,418
Commercial | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021	112,581	1,250,528
2020	986,574	448,704
2019	383,055	296,594
2018	274,606	157,359
2017	151,043	97,036
Prior	187,874	125,361
Revolving loans amortized cost basis	5,709	6,182
Revolving loans converted to term	143,889	136,110
Total Loans	2,245,331	2,517,874
Commercial | Commercial and industrial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,550	3,040
2020	815	26,470
2019	37,613	28,636
2018	28,668	8,482
2017	942	2,577
Prior	18,648	16,993
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	34,036	34,403
Total Loans	122,272	120,601
Commercial | Commercial and industrial | Substandard or Lower
Financing Receivable, Credit Quality Indicator [Line Items]
2021	7,034	82,868
2020	71,567	60,227
2019	58,994	57,880
2018	56,330	50,446
2017	50,763	15,151
Prior	43,356	35,150
Revolving loans amortized cost basis	62	63
Revolving loans converted to term	7,763	9,043
Total Loans	295,869	310,828
Commercial | Owner-occupied commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	40,792	225,393
2020	240,957	245,077
2019	234,026	107,625
2018	100,992	173,364
2017	171,404	139,603
Prior	399,248	292,414
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	146,570	149,251
Total Loans	1,333,989	1,332,727	1,313,193
Gross loans	1,333,989	1,332,727
Commercial | Owner-occupied commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021	40,014	220,165
2020	232,324	225,766
2019	212,673	90,515
2018	84,860	135,903
2017	142,445	123,897
Prior	363,429	271,086
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	121,496	123,194
Total Loans	1,197,241	1,190,526
Commercial | Owner-occupied commercial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	778	1,525
2020	1,174	5,885
2019	5,835	1,838
2018	1,705	17,578
2017	9,044	4,125
Prior	6,757	1,997
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	14,262	14,467
Total Loans	39,555	47,415
Commercial | Owner-occupied commercial | Substandard or Lower
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	3,703
2020	7,459	13,426
2019	15,518	15,272
2018	14,427	19,883
2017	19,915	11,581
Prior	29,062	19,331
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	10,812	11,590
Total Loans	97,193	94,786
Commercial | Commercial mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2021	110,467	414,259
2020	374,563	310,180
2019	294,584	264,939
2018	174,371	281,028
2017	266,449	259,296
Prior	570,679	406,280
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	184,853	150,080
Total Loans	1,975,966	2,086,062	2,223,117
Gross loans	1,975,966	2,086,062
Commercial | Commercial mortgages | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021	109,202	379,592
2020	353,005	283,004
2019	267,193	240,924
2018	170,932	257,809
2017	243,730	254,780
Prior	537,153	375,473
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	182,473	148,210
Total Loans	1,863,688	1,939,792
Commercial | Commercial mortgages | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,265	8,324
2020	8,246	1,774
2019	1,760	21,762
2018	1,203	21,269
2017	21,144	1,274
Prior	7,689	6,507
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	1,860	1,870
Total Loans	43,167	62,780
Commercial | Commercial mortgages | Substandard or Lower
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	26,343
2020	13,312	25,402
2019	25,631	2,253
2018	2,236	1,950
2017	1,575	3,242
Prior	25,837	24,300
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	520	0
Total Loans	69,111	83,490
Commercial | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	51,753	189,257
2020	225,201	223,604
2019	222,131	208,981
2018	178,058	14,929
2017	14,909	7,414
Prior	10,560	3,724
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	81,489	68,366
Total Loans	784,101	716,275	626,253
Gross loans	784,101	716,275
Commercial | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021	39,632	189,257
2020	224,919	214,956
2019	212,469	208,981
2018	178,058	11,414
2017	11,294	7,414
Prior	10,487	3,645
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	79,160	66,018
Total Loans	756,019	701,685
Commercial | Construction | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	7,921	0
2020	0	0
2019	0	0
2018	0	3,515
2017	3,515	0
Prior	0	0
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	0	0
Total Loans	11,436	3,515
Commercial | Construction | Substandard or Lower
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,200	0
2020	282	8,648
2019	9,662	0
2018	0	0
2017	100	0
Prior	73	79
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	2,329	2,348
Total Loans	16,646	11,075
Commercial | Paycheck Protection Program, CARES Act
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	526,800	751,200
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,380	42,588
2020	31,287	26,309
2019	20,546	71,410
2018	58,477	85,277
2017	72,099	149,926
Prior	487,791	388,883
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	0	0
Total Loans	671,580	764,393	955,765
Gross loans	681,022	774,455
Residential | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,380	42,475
2020	31,174	26,309
2019	20,546	71,410
2018	58,477	85,277
2017	72,036	149,643
Prior	482,317	383,358
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	0	0
Total Loans	665,930	758,472
Residential | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	113
2020	113	0
2019	0	0
2018	0	0
2017	63	283
Prior	5,474	5,525
Revolving loans amortized cost basis	0	0
Revolving loans converted to term	0	0
Total Loans	5,650	5,921
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021	19,777	235,948
2020	259,801	134,064
2019	116,206	251,723
2018	228,919	63,945
2017	55,432	44,700
Prior	85,986	53,717
Revolving loans amortized cost basis	365,651	373,238
Revolving loans converted to term	8,262	8,582
Total Loans	1,140,034	1,165,917	$ 1,118,286
Gross loans	1,140,034	1,165,917
Consumer | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2021	19,777	235,948
2020	259,801	134,064
2019	116,173	251,087
2018	228,290	63,713
2017	55,206	44,700
Prior	85,986	53,717
Revolving loans amortized cost basis	364,272	371,842
Revolving loans converted to term	7,880	8,287
Total Loans	1,137,385	1,163,358
Consumer | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	33	636
2018	629	232
2017	226	0
Prior	0	0
Revolving loans amortized cost basis	1,379	1,396
Revolving loans converted to term	382	295
Total Loans	$ 2,649	$ 2,559