Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 5,944	$ 6,282
Allowance for loans collectively evaluated for impairment	134,786	179,545
Allowance for loan commitments	5,766	9,514	$ 10,685	$ 874
Total allowance for credit losses - loans and commitments	146,496	195,341	179,160	53,303
Individually evaluated for credit loss	43,061	44,690
Collectively-evaluated for credit losses	10,314,131	10,744,543
Total loans	10,357,192	10,789,233
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	1,505	1,484
Allowance for loans collectively evaluated for impairment	27,959	36,366
Allowance for loan commitments	941	1,275	1,862	311
Total allowance for credit losses - loans and commitments	30,405	39,125	45,494	14,427
Individually evaluated for credit loss	1,820	2,863
Collectively-evaluated for credit losses	2,117,366	2,404,575
Total loans	2,119,186	2,407,438
Deposit Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	1,056	639
Total allowance for credit losses - loans and commitments	1,056	639	929	1,387
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,705,246	5,705,392
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	466	602
Allowance for loans collectively evaluated for impairment	5,723	10,239
Allowance for loan commitments	3,579	6,508	8,060	235
Total allowance for credit losses - loans and commitments	9,768	17,349	18,395	5,184
Individually evaluated for credit loss	1,334	1,455
Collectively-evaluated for credit losses	586,884	666,822
Total loans	588,218	668,277
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	3,973	4,196
Allowance for loans collectively evaluated for impairment	81,418	106,456
Allowance for loan commitments	94	712		22
Total allowance for credit losses - loans and commitments	85,485	111,364	90,600	20,315
Individually evaluated for credit loss	39,907	40,372
Collectively-evaluated for credit losses	5,077,121	4,996,743
Total loans	5,117,028	5,037,115
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	13,617	17,851
Allowance for loan commitments	1,066	955	713	15
Total allowance for credit losses - loans and commitments	14,683	18,806	14,537	4,326
Collectively-evaluated for credit losses	1,625,632	1,720,961
Total loans	1,625,632	1,720,961
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	4,179	6,507
Allowance for loan commitments	36	19		41
Total allowance for credit losses - loans and commitments	4,215	6,526	7,255	2,992
Collectively-evaluated for credit losses	276,069	309,055
Total loans	276,069	309,055
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	834	1,487
Allowance for loan commitments	50	45	50	250
Total allowance for credit losses - loans and commitments	884	1,532	$ 1,950	$ 4,672
Collectively-evaluated for credit losses	631,059	646,387
Total loans	$ 631,059	$ 646,387