CREDIT QUALITY ASSESSMENT - Allowance for Credit Losses by Respective Loan Portfolio Segment (Detail) - USD ($) $ in Thousands		12 Months Ended
	Apr. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 165,367	$ 56,132	$ 53,486
Initial allowance on Revere PCD loans	$ 18,600	0	18,628	0
Provision/ (credit)		(45,556)	85,669	4,684
Charge-offs		(12,313)	(1,819)	(2,668)
Recoveries		1,647	1,012	630
Net (charge-offs)/ recoveries		(10,666)	(807)
Balance at period end		109,145	165,367	56,132
Total loans		$ 9,967,091	$ 10,400,509
Allowance for credit losses to total loans ratio		1.10%	1590.00%
Average loans		$ 10,034,866	$ 9,317,493
Net charge-offs/ (recoveries) to average loans		0.11%	0.01%
Balance of loans individually evaluated for credit loss		$ 33,534	$ 97,718
Allowance related to loans evaluated individually		$ 6,593	$ 11,405
Individual allowance to loans evaluated individually ratio		19.66%	11670.00%
Balance of loans collectively evaluated for credit loss		$ 9,933,557	$ 10,302,791
Allowance related to loans evaluated collectively		$ 102,552	$ 153,962
Collective allowance to loans evaluated collectively ratio		1.03%	1490.00%
Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 0	$ 2,762	0
Balance at period end			0	2,762
Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		0	2,983	0
Balance at period end			0	2,983
Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs		(5,802)	(411)
Total loans		4,141,346	3,634,720
Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs		(136)	0
Total loans		1,690,881	1,642,216
Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs		(2,007)	0
Total loans		1,088,094	1,050,973
Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs		0	(484)
Total loans		937,570	1,105,179
Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs		0	0
Total loans		197,652	182,619
Commercial real estate: | Commercial investor real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		57,404	18,407
Initial allowance on Revere PCD loans			7,973
Provision/ (credit)		(6,598)	33,431
Charge-offs		(5,802)	(411)
Recoveries		285	15
Net (charge-offs)/ recoveries		(5,517)	(396)
Balance at period end		45,289	57,404	18,407
Total loans		$ 4,141,346	$ 3,634,720
Allowance for credit losses to total loans ratio		1.09%	1580.00%
Average loans		$ 3,689,769	$ 3,210,527
Net charge-offs/ (recoveries) to average loans		0.15%	0.01%
Balance of loans individually evaluated for credit loss		$ 12,489	$ 45,227
Allowance related to loans evaluated individually		$ 213	$ 1,273
Individual allowance to loans evaluated individually ratio		1.71%	2810.00%
Balance of loans collectively evaluated for credit loss		$ 4,128,857	$ 3,589,493
Allowance related to loans evaluated collectively		$ 45,076	$ 56,131
Collective allowance to loans evaluated collectively ratio		1.09%	1560.00%
Commercial real estate: | Commercial investor real estate | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 1,114
Balance at period end				1,114
Commercial real estate: | Commercial investor real estate | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			(3,125)
Balance at period end				(3,125)
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 20,061	6,884
Initial allowance on Revere PCD loans			2,782
Provision/ (credit)		(8,238)	10,008
Charge-offs		(136)	0
Recoveries		0	0
Net (charge-offs)/ recoveries		(136)	0
Balance at period end		11,687	20,061	6,884
Total loans		$ 1,690,881	$ 1,642,216
Allowance for credit losses to total loans ratio		0.69%	1220.00%
Average loans		$ 1,661,015	$ 1,560,223
Net charge-offs/ (recoveries) to average loans		0.01%	0.00%
Balance of loans individually evaluated for credit loss		$ 9,306	$ 11,561
Allowance related to loans evaluated individually		$ 79	$ 0
Individual allowance to loans evaluated individually ratio		0.85%	0.00%
Balance of loans collectively evaluated for credit loss		$ 1,681,575	$ 1,630,655
Allowance related to loans evaluated collectively		$ 11,608	$ 20,061
Collective allowance to loans evaluated collectively ratio		0.69%	1230.00%
Commercial real estate: | Commercial owner-occupied real estate | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 0
Balance at period end				0
Commercial real estate: | Commercial owner-occupied real estate | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			387
Balance at period end				387
Commercial real estate: | Commercial AD&C
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 22,157	7,590
Initial allowance on Revere PCD loans			1,248
Provision/ (credit)		172	10,743
Charge-offs		(2,007)	0
Recoveries		0	0
Net (charge-offs)/ recoveries		(2,007)	0
Balance at period end		20,322	22,157	7,590
Total loans		$ 1,088,094	$ 1,050,973
Allowance for credit losses to total loans ratio		1.87%	2110.00%
Average loans		$ 1,110,420	$ 906,414
Net charge-offs/ (recoveries) to average loans		0.18%	0.00%
Balance of loans individually evaluated for credit loss		$ 650	$ 15,044
Allowance related to loans evaluated individually		$ 504	$ 603
Individual allowance to loans evaluated individually ratio		77.54%	4010.00%
Balance of loans collectively evaluated for credit loss		$ 1,087,444	$ 1,035,929
Allowance related to loans evaluated collectively		$ 19,818	$ 21,554
Collective allowance to loans evaluated collectively ratio		1.82%	2080.00%
Commercial real estate: | Commercial AD&C | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 0
Balance at period end				0
Commercial real estate: | Commercial AD&C | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			2,576
Balance at period end				2,576
Commercial Business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Total loans		$ 8,402,155	8,595,457
Balance of loans individually evaluated for credit loss		9,033	23,648
Allowance related to loans evaluated individually		5,797	9,529
Commercial Business | Commercial business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		46,806	11,395
Initial allowance on Revere PCD loans			6,289
Provision/ (credit)		(20,132)	24,374
Charge-offs		(4,069)	(491)
Recoveries		565	702
Net (charge-offs)/ recoveries		(3,504)	211
Balance at period end		23,170	46,806	11,395
Total loans		$ 1,481,834	$ 2,267,548
Allowance for credit losses to total loans ratio		1.56%	2060.00%
Average loans		$ 1,952,537	$ 1,781,197
Net charge-offs/ (recoveries) to average loans		0.18%	(0.01%)
Balance of loans individually evaluated for credit loss		$ 9,033	$ 23,648
Allowance related to loans evaluated individually		$ 5,797	$ 9,529
Individual allowance to loans evaluated individually ratio		64.18%	40300.00%
Balance of loans collectively evaluated for credit loss		$ 1,472,801	$ 2,243,900
Allowance related to loans evaluated collectively		$ 17,373	$ 37,277
Collective allowance to loans evaluated collectively ratio		1.18%	1660.00%
Commercial Business | Commercial business | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 1,549
Balance at period end				1,549
Commercial Business | Commercial business | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			2,988
Balance at period end				2,988
Residential real estate: | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 11,295	8,803
Initial allowance on Revere PCD loans			243
Provision/ (credit)		(6,321)	3,016
Charge-offs		0	(484)
Recoveries		410	105
Net (charge-offs)/ recoveries		410	(379)
Balance at period end		5,384	11,295	8,803
Total loans		$ 937,570	$ 1,105,179
Allowance for credit losses to total loans ratio		0.57%	1020.00%
Average loans		$ 979,754	$ 1,168,668
Net charge-offs/ (recoveries) to average loans		(0.04%)	0.03%
Balance of loans individually evaluated for credit loss		$ 1,704	$ 1,874
Allowance related to loans evaluated individually		$ 0	$ 0
Individual allowance to loans evaluated individually ratio		0.00%	0.00%
Balance of loans collectively evaluated for credit loss		$ 935,866	$ 1,103,305
Allowance related to loans evaluated collectively		$ 5,384	$ 11,295
Collective allowance to loans evaluated collectively ratio		0.58%	1020.00%
Residential real estate: | Residential mortgage | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 0
Balance at period end				0
Residential real estate: | Residential mortgage | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			(388)
Balance at period end				(388)
Residential real estate: | Residential construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 1,502	967
Initial allowance on Revere PCD loans			6
Provision/ (credit)		(459)	798
Charge-offs		0	0
Recoveries		5	6
Net (charge-offs)/ recoveries		5	6
Balance at period end		1,048	1,502	967
Total loans		$ 197,652	$ 182,619
Allowance for credit losses to total loans ratio		0.53%	820.00%
Average loans		$ 178,171	$ 165,567
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%
Balance of loans collectively evaluated for credit loss		$ 197,652	$ 182,619
Allowance related to loans evaluated collectively		$ 1,048	$ 1,502
Collective allowance to loans evaluated collectively ratio		0.53%	820.00%
Residential real estate: | Residential construction | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 0
Balance at period end				0
Residential real estate: | Residential construction | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			(275)
Balance at period end				(275)
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year		$ 6,142	2,086
Initial allowance on Revere PCD loans			87
Provision/ (credit)		(3,980)	3,299
Charge-offs		(299)	(433)
Recoveries		382	184
Net (charge-offs)/ recoveries		83	(249)
Balance at period end		2,245	6,142	2,086
Total loans		$ 429,714	$ 517,254
Allowance for credit losses to total loans ratio		0.52%	1190.00%
Average loans		$ 463,200	$ 524,897
Net charge-offs/ (recoveries) to average loans		(0.02%)	0.05%
Balance of loans individually evaluated for credit loss		$ 352	$ 364
Allowance related to loans evaluated individually		$ 0	$ 0
Individual allowance to loans evaluated individually ratio		0.00%	0.00%
Balance of loans collectively evaluated for credit loss		$ 429,362	$ 516,890
Allowance related to loans evaluated collectively		$ 2,245	$ 6,142
Collective allowance to loans evaluated collectively ratio		0.52%	1190.00%
Consumer | Revision of Prior Period, Reclassification, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 99
Balance at period end				99
Consumer | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year			$ 820
Balance at period end				$ 820