Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 6,039	$ 6,282
Allowance for loans collectively evaluated for impairment	154,001	179,545
Allowance for loan commitments	6,731	9,514	$ 5,572	$ 874
Total allowance for credit losses - loans and commitments	166,771	195,341	119,844	53,303
Individually evaluated for credit loss	43,121	44,690
Collectively-evaluated for credit losses	10,660,191	10,744,543
Total loans	10,703,312	10,789,233
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	1,501	1,484
Allowance for loans collectively evaluated for impairment	31,783	36,366
Allowance for loan commitments	1,583	1,275		311
Total allowance for credit losses - loans and commitments	34,867	39,125	39,227	14,427
Individually evaluated for credit loss	1,838	2,863
Collectively-evaluated for credit losses	2,420,897	2,404,575
Total loans	2,422,735	2,407,438
Deposit Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	707	639
Total allowance for credit losses - loans and commitments	707	639	1,064	1,387
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,712,742	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	503	602
Allowance for loans collectively evaluated for impairment	6,837	10,239
Allowance for loan commitments	4,000	6,508	5,111	235
Total allowance for credit losses - loans and commitments	11,340	17,349	11,553	5,184
Individually evaluated for credit loss	1,125	1,455
Collectively-evaluated for credit losses	640,892	666,822
Total loans	642,017	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	4,035	4,196
Allowance for loans collectively evaluated for impairment	95,706	106,456
Allowance for loan commitments	208	712		22
Total allowance for credit losses - loans and commitments	99,949	111,364	52,873	20,315
Individually evaluated for credit loss	40,158	40,372
Collectively-evaluated for credit losses	5,030,567	4,996,743
Total loans	5,070,725	5,037,115
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	13,438	17,851
Allowance for loan commitments	869	955	444	15
Total allowance for credit losses - loans and commitments	14,307	18,806	10,128	4,326
Collectively-evaluated for credit losses	1,644,422	1,720,961
Total loans	1,644,422	1,720,961
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	4,532	6,507
Allowance for loan commitments	21	19		41
Total allowance for credit losses - loans and commitments	4,553	6,526	3,886	2,992
Collectively-evaluated for credit losses	289,395	309,055
Total loans	289,395	309,055
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	998	1,487
Allowance for loan commitments	50	45	17	250
Total allowance for credit losses - loans and commitments	1,048	1,532	$ 1,113	$ 4,672
Collectively-evaluated for credit losses	634,018	646,387
Total loans	$ 634,018	$ 646,387

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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