Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 6,282	$ 124
Allowance for loans collectively evaluated for impairment	179,545	52,305
Allowance for loan commitments	9,514	874	$ 741	$ 574
Total allowance for credit losses - loans and commitments	195,341	53,303	49,689	45,858
Individually evaluated for credit loss	44,690	21,017
Collectively-evaluated for credit losses	10,744,543	10,232,455
Acquired with deteriorated credit quality		14,513
Total loans	10,789,233	10,267,985
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	1,484	10
Allowance for loans collectively evaluated for impairment	36,366	14,106
Allowance for loan commitments	1,275	311	262	173
Total allowance for credit losses - loans and commitments	39,125	14,427	12,376	9,587
Individually evaluated for credit loss	2,863	11,961
Collectively-evaluated for credit losses	2,404,575	1,631,855
Acquired with deteriorated credit quality		883
Total loans	2,407,438	1,644,699
Deposit Overdraft [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	639	1,387
Total allowance for credit losses - loans and commitments	639	1,387	972	821
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,705,392	5,725,008
Commercial Real Estate [Member] \| Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	602
Allowance for loans collectively evaluated for impairment	10,239	4,949
Allowance for loan commitments	6,508	235	169	119
Total allowance for credit losses - loans and commitments	17,349	5,184	4,208	3,236
Individually evaluated for credit loss	1,455
Collectively-evaluated for credit losses	666,822	777,033
Acquired with deteriorated credit quality		118
Total loans	668,277	777,151
Commercial Real Estate [Member] \| Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	4,196	93
Allowance for loans collectively evaluated for impairment	106,456	20,200
Allowance for loan commitments	712	22	33	26
Total allowance for credit losses - loans and commitments	111,364	20,315	20,881	21,192
Individually evaluated for credit loss	40,372	3,907
Collectively-evaluated for credit losses	4,996,743	4,935,383
Acquired with deteriorated credit quality		8,567
Total loans	5,037,115	4,947,857
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		14
Allowance for loans collectively evaluated for impairment	17,851	4,297
Allowance for loan commitments	955	15	12	7
Total allowance for credit losses - loans and commitments	18,806	4,326	3,834	3,213
Individually evaluated for credit loss		4,392
Collectively-evaluated for credit losses	1,720,961	1,865,151
Acquired with deteriorated credit quality		4,104
Total loans	1,720,961	1,873,647
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		1
Allowance for loans collectively evaluated for impairment	6,507	2,950
Allowance for loan commitments	19	41	39	37
Total allowance for credit losses - loans and commitments	6,526	2,992	2,836	3,100
Individually evaluated for credit loss		53
Collectively-evaluated for credit losses	309,055	374,812
Acquired with deteriorated credit quality		88
Total loans	309,055	374,953
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		6
Allowance for loans collectively evaluated for impairment	1,487	4,416
Allowance for loan commitments	45	250	226	212
Total allowance for credit losses - loans and commitments	1,532	4,672	$ 4,582	$ 4,709
Individually evaluated for credit loss		704
Collectively-evaluated for credit losses	646,387	648,221
Acquired with deteriorated credit quality		753
Total loans	$ 646,387	$ 649,678

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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