Loans and the Allowance for Credit Losses - Summary of Amortized Cost Basis Loan Balances by Year of Origination and Credit Quality Indicator (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Portfolio loans, net of unearned income	$ 10,349,596		$ 10,267,985
Current-period gross write-offs	(6,126)	$ (2,636)
Current-period recoveries	1,410	1,266
Net charge-offs	(4,716)	(1,370)
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	5,675
Amortized Cost Basis by Origination Year 2019	5,286
Amortized Cost Basis by Origination Year 2018	6,023
Amortized Cost Basis by Origination Year 2017	1,647
Amortized Cost Basis by Origination Year 2016	1,560
Amortized Cost Basis by Origination Year, Prior to 2016	63,331
Revolving Loans	552,324
Revolving Loans Converted to Term	14,908
Portfolio loans, net of unearned income	650,754		649,678
Current-period gross write-offs	(443)	(357)
Current-period recoveries	172	47
Amortized Cost Basis by Origination Year , Current-period net write-offs Prior to 2016	60
Revolving Loans, Current period net write-offs	(302)
Revolving Loans Converted to Term, Current period net write-offs	(29)
Net charge-offs	(271)	(310)
Home Equity [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	5,675
Amortized Cost Basis by Origination Year 2019	5,276
Amortized Cost Basis by Origination Year 2018	6,006
Amortized Cost Basis by Origination Year 2017	1,633
Amortized Cost Basis by Origination Year 2016	1,414
Amortized Cost Basis by Origination Year, Prior to 2016	59,756
Revolving Loans	549,310
Revolving Loans Converted to Term	13,836
Portfolio loans, net of unearned income	642,906
Home Equity [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	10
Amortized Cost Basis by Origination Year 2017	11
Amortized Cost Basis by Origination Year, Prior to 2016	933
Revolving Loans	1,829
Revolving Loans Converted to Term	56
Portfolio loans, net of unearned income	2,839
Home Equity [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2017	3
Amortized Cost Basis by Origination Year 2016	57
Amortized Cost Basis by Origination Year, Prior to 2016	305
Revolving Loans	245
Revolving Loans Converted to Term	249
Portfolio loans, net of unearned income	859
Home Equity [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	17
Amortized Cost Basis by Origination Year 2016	89
Amortized Cost Basis by Origination Year, Prior to 2016	2,337
Revolving Loans	940
Revolving Loans Converted to Term	767
Portfolio loans, net of unearned income	4,150
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Portfolio loans, net of unearned income	5,604,405		5,725,008
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	58,725
Amortized Cost Basis by Origination Year 2019	320,602
Amortized Cost Basis by Origination Year 2018	249,487
Amortized Cost Basis by Origination Year 2017	166,863
Amortized Cost Basis by Origination Year 2016	219,762
Amortized Cost Basis by Origination Year, Prior to 2016	910,196
Revolving Loans	3,955
Portfolio loans, net of unearned income	1,929,590		1,873,647
Current-period gross write-offs	(386)	(320)
Current-period recoveries	272	121
Amortized Cost Basis by Origination Year , Current-period net write-offs 2019	(24)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2018	(8)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2016	(19)
Amortized Cost Basis by Origination Year , Current-period net write-offs Prior to 2016	(63)
Net charge-offs	(114)	(199)
Residential Real Estate [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	58,725
Amortized Cost Basis by Origination Year 2019	320,536
Amortized Cost Basis by Origination Year 2018	248,330
Amortized Cost Basis by Origination Year 2017	166,863
Amortized Cost Basis by Origination Year 2016	218,233
Amortized Cost Basis by Origination Year, Prior to 2016	891,597
Revolving Loans	3,955
Portfolio loans, net of unearned income	1,908,239
Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	217
Amortized Cost Basis by Origination Year 2016	248
Amortized Cost Basis by Origination Year, Prior to 2016	4,944
Portfolio loans, net of unearned income	5,409
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	700
Amortized Cost Basis by Origination Year 2016	109
Amortized Cost Basis by Origination Year, Prior to 2016	1,400
Portfolio loans, net of unearned income	2,209
Residential Real Estate [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	66
Amortized Cost Basis by Origination Year 2018	240
Amortized Cost Basis by Origination Year 2016	1,172
Amortized Cost Basis by Origination Year, Prior to 2016	12,255
Portfolio loans, net of unearned income	13,733
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	22,562
Amortized Cost Basis by Origination Year 2019	124,618
Amortized Cost Basis by Origination Year 2018	58,219
Amortized Cost Basis by Origination Year 2017	35,740
Amortized Cost Basis by Origination Year 2016	22,713
Amortized Cost Basis by Origination Year, Prior to 2016	74,306
Revolving Loans	24,736
Revolving Loans Converted to Term	202
Portfolio loans, net of unearned income	363,096		374,953
Current-period gross write-offs	(856)	(661)
Current-period recoveries	415	411
Amortized Cost Basis by Origination Year , Current-period net write-offs 2019	(219)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2018	(136)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2017	(76)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2016	(64)
Amortized Cost Basis by Origination Year , Current-period net write-offs Prior to 2016	54
Net charge-offs	(441)	(250)
Consumer [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	22,559
Amortized Cost Basis by Origination Year 2019	124,073
Amortized Cost Basis by Origination Year 2018	57,611
Amortized Cost Basis by Origination Year 2017	34,864
Amortized Cost Basis by Origination Year 2016	22,298
Amortized Cost Basis by Origination Year, Prior to 2016	72,797
Revolving Loans	24,705
Revolving Loans Converted to Term	202
Portfolio loans, net of unearned income	359,109
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	3
Amortized Cost Basis by Origination Year 2019	271
Amortized Cost Basis by Origination Year 2018	373
Amortized Cost Basis by Origination Year 2017	491
Amortized Cost Basis by Origination Year 2016	290
Amortized Cost Basis by Origination Year, Prior to 2016	1,008
Revolving Loans	6
Portfolio loans, net of unearned income	2,442
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	89
Amortized Cost Basis by Origination Year 2018	193
Amortized Cost Basis by Origination Year 2017	154
Amortized Cost Basis by Origination Year 2016	48
Amortized Cost Basis by Origination Year, Prior to 2016	201
Revolving Loans	5
Portfolio loans, net of unearned income	690
Consumer [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	185
Amortized Cost Basis by Origination Year 2018	42
Amortized Cost Basis by Origination Year 2017	231
Amortized Cost Basis by Origination Year 2016	77
Amortized Cost Basis by Origination Year, Prior to 2016	300
Revolving Loans	20
Portfolio loans, net of unearned income	855
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	45,030
Amortized Cost Basis by Origination Year 2019	226,205
Amortized Cost Basis by Origination Year 2018	194,610
Amortized Cost Basis by Origination Year 2017	66,134
Amortized Cost Basis by Origination Year 2016	21,398
Amortized Cost Basis by Origination Year, Prior to 2016	51,225
Revolving Loans	72,124
Portfolio loans, net of unearned income	676,726		777,151
Current-period gross write-offs	(1)
Current-period recoveries	8	12
Amortized Cost Basis by Origination Year , Current-period net write-offs Prior to 2016	7
Net charge-offs	7	12
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	45,030
Amortized Cost Basis by Origination Year 2019	226,205
Amortized Cost Basis by Origination Year 2018	193,697
Amortized Cost Basis by Origination Year 2017	65,923
Amortized Cost Basis by Origination Year 2016	20,998
Amortized Cost Basis by Origination Year, Prior to 2016	48,284
Revolving Loans	71,905
Portfolio loans, net of unearned income	672,042
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	42
Amortized Cost Basis by Origination Year 2017	211
Amortized Cost Basis by Origination Year 2016	83
Amortized Cost Basis by Origination Year, Prior to 2016	1,176
Revolving Loans	149
Portfolio loans, net of unearned income	1,661
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member] | Classified - substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	871
Amortized Cost Basis by Origination Year 2016	317
Amortized Cost Basis by Origination Year, Prior to 2016	1,765
Revolving Loans	70
Portfolio loans, net of unearned income	3,023
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	191,722
Amortized Cost Basis by Origination Year 2019	752,149
Amortized Cost Basis by Origination Year 2018	631,304
Amortized Cost Basis by Origination Year 2017	671,682
Amortized Cost Basis by Origination Year 2016	762,009
Amortized Cost Basis by Origination Year, Prior to 2016	1,808,557
Revolving Loans	110,256
Portfolio loans, net of unearned income	4,927,679		4,947,857
Current-period gross write-offs	(1,398)	(222)
Current-period recoveries	293	198
Amortized Cost Basis by Origination Year , Current-period net write-offs 2017	12
Amortized Cost Basis by Origination Year , Current-period net write-offs 2016	(1,219)
Amortized Cost Basis by Origination Year , Current-period net write-offs Prior to 2016	102
Net charge-offs	(1,105)	(24)
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	191,722
Amortized Cost Basis by Origination Year 2019	749,290
Amortized Cost Basis by Origination Year 2018	623,215
Amortized Cost Basis by Origination Year 2017	641,275
Amortized Cost Basis by Origination Year 2016	739,260
Amortized Cost Basis by Origination Year, Prior to 2016	1,723,158
Revolving Loans	109,941
Portfolio loans, net of unearned income	4,777,861
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	2,788
Amortized Cost Basis by Origination Year 2018	3,995
Amortized Cost Basis by Origination Year 2017	22,493
Amortized Cost Basis by Origination Year 2016	12,200
Amortized Cost Basis by Origination Year, Prior to 2016	36,321
Revolving Loans	315
Portfolio loans, net of unearned income	78,112
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | Classified - substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	71
Amortized Cost Basis by Origination Year 2018	4,094
Amortized Cost Basis by Origination Year 2017	7,914
Amortized Cost Basis by Origination Year 2016	10,549
Amortized Cost Basis by Origination Year, Prior to 2016	49,078
Portfolio loans, net of unearned income	71,706
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	61,857
Amortized Cost Basis by Origination Year 2019	293,969
Amortized Cost Basis by Origination Year 2018	224,310
Amortized Cost Basis by Origination Year 2017	188,822
Amortized Cost Basis by Origination Year 2016	108,883
Amortized Cost Basis by Origination Year, Prior to 2016	355,807
Revolving Loans	567,942
Revolving Loans Converted to Term	161
Portfolio loans, net of unearned income	1,801,751		$ 1,644,699
Current-period gross write-offs	(2,714)	(635)
Current-period recoveries	107	378
Amortized Cost Basis by Origination Year , Current-period net write-offs 2018	(727)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2017	(170)
Amortized Cost Basis by Origination Year , Current-period net write-offs 2016	(30)
Amortized Cost Basis by Origination Year , Current-period net write-offs Prior to 2016	(276)
Revolving Loans, Current period net write-offs	(1,404)
Net charge-offs	(2,607)	$ (257)
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	61,827
Amortized Cost Basis by Origination Year 2019	291,133
Amortized Cost Basis by Origination Year 2018	220,651
Amortized Cost Basis by Origination Year 2017	183,752
Amortized Cost Basis by Origination Year 2016	106,337
Amortized Cost Basis by Origination Year, Prior to 2016	337,917
Revolving Loans	538,512
Revolving Loans Converted to Term	161
Portfolio loans, net of unearned income	1,740,290
Commercial and Industrial [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	30
Amortized Cost Basis by Origination Year 2019	1,789
Amortized Cost Basis by Origination Year 2018	2,132
Amortized Cost Basis by Origination Year 2017	2,897
Amortized Cost Basis by Origination Year 2016	978
Amortized Cost Basis by Origination Year, Prior to 2016	10,401
Revolving Loans	22,801
Portfolio loans, net of unearned income	41,028
Commercial and Industrial [Member] | Classified - substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	1,047
Amortized Cost Basis by Origination Year 2018	1,527
Amortized Cost Basis by Origination Year 2017	2,173
Amortized Cost Basis by Origination Year 2016	1,568
Amortized Cost Basis by Origination Year, Prior to 2016	7,489
Revolving Loans	6,629
Portfolio loans, net of unearned income	$ 20,433