Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 4,963	$ 3,118
Allowance for loans collectively evaluated for impairment	121,652	114,672
Allowance for loan commitments	9,729	8,368	$ 8,938	$ 7,775
Total allowance for credit losses - loans and commitments	136,344	126,158	123,522	129,397
Individually evaluated for credit loss	27,105	50,399
Collectively-evaluated for credit losses	11,288,768	10,652,329
Total loans	11,315,873	10,702,728
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		130
Allowance for loans collectively evaluated for impairment	34,716	31,410
Allowance for loan commitments	1,087		283	1,497
Total allowance for credit losses - loans and commitments	35,803	31,540	29,206	28,372
Individually evaluated for credit loss	181	401
Collectively-evaluated for credit losses	1,587,430	1,578,994
Total loans	1,587,611	1,579,395
Deposit Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	1,289	1,285
Total allowance for credit losses - loans and commitments	1,289	1,285	1,543	2,220
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	6,387,183	6,061,344
Commercial Real Estate [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	6,108	6,737
Allowance for loan commitments	7,272	6,025	5,798	4,180
Total allowance for credit losses - loans and commitments	13,380	12,762	14,429	11,490
Individually evaluated for credit loss		24,629
Collectively-evaluated for credit losses	870,066	919,258
Total loans	870,066	943,887
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	4,963	2,988
Allowance for loans collectively evaluated for impairment	54,662	49,671
Allowance for loan commitments				201
Total allowance for credit losses - loans and commitments	59,625	52,659	53,530	65,556
Individually evaluated for credit loss	26,924	25,369
Collectively-evaluated for credit losses	5,490,193	5,092,088
Total loans	5,517,117	5,117,457
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	20,441	18,208
Allowance for loan commitments	1,352	2,215	2,364	1,576
Total allowance for credit losses - loans and commitments	21,793	20,423	19,099	16,977
Collectively-evaluated for credit losses	2,392,531	2,140,584
Total loans	2,392,531	2,140,584
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	3,442	3,127
Allowance for loan commitments			437	272
Total allowance for credit losses - loans and commitments	3,442	3,127	4,871	4,009
Collectively-evaluated for credit losses	233,362	226,340
Total loans	233,362	226,340
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	994	4,234
Allowance for loan commitments	18	128	56	49
Total allowance for credit losses - loans and commitments	1,012	4,362	$ 844	$ 773
Collectively-evaluated for credit losses	715,186	695,065
Total loans	$ 715,186	$ 695,065