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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Portfolio loans, net of unearned income	$ 10,789,233	$ 10,267,985
Current-period gross write-offs	(12,535)	(12,657)	$ (10,567)
Current-period recoveries	5,486	5,073	6,634
Net charge-offs	(7,049)	(7,584)	(3,933)
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	18,315
Amortized Cost Basis by Origination Year 2019	3,611
Amortized Cost Basis by Origination Year 2018	3,376
Amortized Cost Basis by Origination Year 2017	1,131
Amortized Cost Basis by Origination Year 2016	1,198
Amortized Cost Basis by Origination Year, Prior to 2016	19,159
Revolving Loans	586,557
Revolving Loans Converted to Term	13,040
Portfolio loans, net of unearned income	646,387	649,678
Current-period gross write-offs	(969)	(1,213)	(1,193)
Current-period recoveries	501	428	914
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2018	(10)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2017	(2)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2016	(1)
Amortized Cost Basis by Origination Year, Current-period net charge-offs Prior to 2016	(92)
Revolving Loans, Current period net charge-offs	(356)
Revolving Loans Converted to Term, Current-period net charge-offs	(7)
Net charge-offs	(468)	(785)	(279)
Home Equity [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	18,191
Amortized Cost Basis by Origination Year 2019	3,611
Amortized Cost Basis by Origination Year 2018	3,334
Amortized Cost Basis by Origination Year 2017	975
Amortized Cost Basis by Origination Year 2016	1,110
Amortized Cost Basis by Origination Year, Prior to 2016	16,477
Revolving Loans	583,486
Revolving Loans Converted to Term	12,135
Portfolio loans, net of unearned income	639,319
Home Equity [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	124
Amortized Cost Basis by Origination Year 2018	34
Amortized Cost Basis by Origination Year, Prior to 2016	882
Revolving Loans	1,247
Revolving Loans Converted to Term	127
Portfolio loans, net of unearned income	2,414
Home Equity [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year, Prior to 2016	14
Revolving Loans	749
Revolving Loans Converted to Term	12
Portfolio loans, net of unearned income	775
Home Equity [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	8
Amortized Cost Basis by Origination Year 2017	156
Amortized Cost Basis by Origination Year 2016	88
Amortized Cost Basis by Origination Year, Prior to 2016	1,786
Revolving Loans	1,075
Revolving Loans Converted to Term	766
Portfolio loans, net of unearned income	3,879
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Portfolio loans, net of unearned income	5,705,392	5,725,008
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	385,541
Amortized Cost Basis by Origination Year 2019	243,253
Amortized Cost Basis by Origination Year 2018	150,912
Amortized Cost Basis by Origination Year 2017	109,384
Amortized Cost Basis by Origination Year 2016	171,971
Amortized Cost Basis by Origination Year, Prior to 2016	659,900
Portfolio loans, net of unearned income	1,720,961	1,873,647
Current-period gross write-offs	(1,415)	(1,276)	(1,435)
Current-period recoveries	640	365	439
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2019	(24)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2018	(8)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2017	(11)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2016	(110)
Amortized Cost Basis by Origination Year, Current-period net charge-offs Prior to 2016	(622)
Net charge-offs	(775)	(911)	(996)
Residential Real Estate [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	385,541
Amortized Cost Basis by Origination Year 2019	242,770
Amortized Cost Basis by Origination Year 2018	149,603
Amortized Cost Basis by Origination Year 2017	108,090
Amortized Cost Basis by Origination Year 2016	170,967
Amortized Cost Basis by Origination Year, Prior to 2016	641,665
Portfolio loans, net of unearned income	1,698,636
Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	320
Amortized Cost Basis by Origination Year 2017	533
Amortized Cost Basis by Origination Year, Prior to 2016	1,761
Portfolio loans, net of unearned income	2,614
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	823
Amortized Cost Basis by Origination Year 2016	185
Amortized Cost Basis by Origination Year, Prior to 2016	4,646
Portfolio loans, net of unearned income	5,654
Residential Real Estate [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	483
Amortized Cost Basis by Origination Year 2018	166
Amortized Cost Basis by Origination Year 2017	761
Amortized Cost Basis by Origination Year 2016	819
Amortized Cost Basis by Origination Year, Prior to 2016	11,828
Portfolio loans, net of unearned income	14,057
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	73,714
Amortized Cost Basis by Origination Year 2019	90,264
Amortized Cost Basis by Origination Year 2018	39,951
Amortized Cost Basis by Origination Year 2017	22,560
Amortized Cost Basis by Origination Year 2016	13,513
Amortized Cost Basis by Origination Year, Prior to 2016	46,609
Revolving Loans	22,279
Revolving Loans Converted to Term	165
Portfolio loans, net of unearned income	309,055	374,953
Current-period gross write-offs	(3,615)	(2,719)	(3,508)
Current-period recoveries	1,574	1,743	2,100
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2020	(273)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2019	(731)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2018	(589)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2017	(486)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2016	(59)
Amortized Cost Basis by Origination Year, Current-period net charge-offs Prior to 2016	97
Net charge-offs	(2,041)	(976)	(1,408)
Consumer [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	72,847
Amortized Cost Basis by Origination Year 2019	89,637
Amortized Cost Basis by Origination Year 2018	39,584
Amortized Cost Basis by Origination Year 2017	22,118
Amortized Cost Basis by Origination Year 2016	13,144
Amortized Cost Basis by Origination Year, Prior to 2016	45,735
Revolving Loans	22,253
Revolving Loans Converted to Term	165
Portfolio loans, net of unearned income	305,483
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	481
Amortized Cost Basis by Origination Year 2019	408
Amortized Cost Basis by Origination Year 2018	210
Amortized Cost Basis by Origination Year 2017	311
Amortized Cost Basis by Origination Year 2016	194
Amortized Cost Basis by Origination Year, Prior to 2016	379
Revolving Loans	15
Portfolio loans, net of unearned income	1,998
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	273
Amortized Cost Basis by Origination Year 2019	147
Amortized Cost Basis by Origination Year 2018	84
Amortized Cost Basis by Origination Year 2017	100
Amortized Cost Basis by Origination Year 2016	163
Amortized Cost Basis by Origination Year, Prior to 2016	253
Revolving Loans	11
Portfolio loans, net of unearned income	1,031
Consumer [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	113
Amortized Cost Basis by Origination Year 2019	72
Amortized Cost Basis by Origination Year 2018	73
Amortized Cost Basis by Origination Year 2017	31
Amortized Cost Basis by Origination Year 2016	12
Amortized Cost Basis by Origination Year, Prior to 2016	242
Portfolio loans, net of unearned income	543
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	134,179
Amortized Cost Basis by Origination Year 2019	314,614
Amortized Cost Basis by Origination Year 2018	111,167
Amortized Cost Basis by Origination Year 2017	27,774
Amortized Cost Basis by Origination Year 2016	16,774
Amortized Cost Basis by Origination Year, Prior to 2016	36,156
Revolving Loans	27,613
Portfolio loans, net of unearned income	668,277	777,151
Current-period gross write-offs	(51)	(107)	(137)
Current-period recoveries	92	271	409
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2017	61
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2016	(50)
Amortized Cost Basis by Origination Year, Current-period net charge-offs Prior to 2016	30
Net charge-offs	41	164	272
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	133,720
Amortized Cost Basis by Origination Year 2019	314,614
Amortized Cost Basis by Origination Year 2018	109,232
Amortized Cost Basis by Origination Year 2017	27,483
Amortized Cost Basis by Origination Year 2016	16,404
Amortized Cost Basis by Origination Year, Prior to 2016	29,685
Revolving Loans	26,297
Portfolio loans, net of unearned income	657,435
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 2020	459
Amortized Cost Basis by Origination Year 2018	1,532
Amortized Cost Basis by Origination Year 2017	233
Amortized Cost Basis by Origination Year 2016	79
Amortized Cost Basis by Origination Year, Prior to 2016	3,778
Revolving Loans	1,316
Portfolio loans, net of unearned income	7,397
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	403
Amortized Cost Basis by Origination Year 2017	58
Amortized Cost Basis by Origination Year 2016	291
Amortized Cost Basis by Origination Year, Prior to 2016	2,693
Portfolio loans, net of unearned income	3,445
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	812,311
Amortized Cost Basis by Origination Year 2019	754,181
Amortized Cost Basis by Origination Year 2018	668,368
Amortized Cost Basis by Origination Year 2017	545,520
Amortized Cost Basis by Origination Year 2016	633,477
Amortized Cost Basis by Origination Year, Prior to 2016	1,532,366
Revolving Loans	90,892
Portfolio loans, net of unearned income	5,037,115	4,947,857
Current-period gross write-offs	(1,747)	(3,867)	(1,090)
Current-period recoveries	796	752	1,293
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2018	(38)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2017	13
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2016	(1,617)
Amortized Cost Basis by Origination Year, Current-period net charge-offs Prior to 2016	691
Net charge-offs	(951)	(3,115)	203
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	809,516
Amortized Cost Basis by Origination Year 2019	670,554
Amortized Cost Basis by Origination Year 2018	646,629
Amortized Cost Basis by Origination Year 2017	474,622
Amortized Cost Basis by Origination Year 2016	572,733
Amortized Cost Basis by Origination Year, Prior to 2016	1,346,552
Revolving Loans	89,120
Portfolio loans, net of unearned income	4,609,726
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	2,693
Amortized Cost Basis by Origination Year 2019	67,261
Amortized Cost Basis by Origination Year 2018	16,793
Amortized Cost Basis by Origination Year 2017	59,251
Amortized Cost Basis by Origination Year 2016	42,284
Amortized Cost Basis by Origination Year, Prior to 2016	130,247
Revolving Loans	1,772
Portfolio loans, net of unearned income	320,301
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 2020	102
Amortized Cost Basis by Origination Year 2019	16,366
Amortized Cost Basis by Origination Year 2018	4,946
Amortized Cost Basis by Origination Year 2017	11,647
Amortized Cost Basis by Origination Year 2016	18,460
Amortized Cost Basis by Origination Year, Prior to 2016	55,567
Portfolio loans, net of unearned income	107,088
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	977,538
Amortized Cost Basis by Origination Year 2019	246,805
Amortized Cost Basis by Origination Year 2018	199,865
Amortized Cost Basis by Origination Year 2017	167,490
Amortized Cost Basis by Origination Year 2016	87,306
Amortized Cost Basis by Origination Year, Prior to 2016	282,603
Revolving Loans	445,695
Revolving Loans Converted to Term	136
Portfolio loans, net of unearned income	2,407,438	1,644,699
Current-period gross write-offs	(3,727)	(1,816)	(1,830)
Current-period recoveries	1,457	1,104	1,100
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2019	(50)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2018	(1,843)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2017	(272)
Amortized Cost Basis by Origination Year, Current-period net charge-offs 2016	(108)
Amortized Cost Basis by Origination Year, Current-period net charge-offs Prior to 2016	303
Revolving Loans, Current period net charge-offs	(300)
Net charge-offs	(2,270)	$ (712)	$ (730)
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	977,085
Amortized Cost Basis by Origination Year 2019	240,262
Amortized Cost Basis by Origination Year 2018	193,712
Amortized Cost Basis by Origination Year 2017	160,924
Amortized Cost Basis by Origination Year 2016	85,379
Amortized Cost Basis by Origination Year, Prior to 2016	265,890
Revolving Loans	427,336
Revolving Loans Converted to Term	136
Portfolio loans, net of unearned income	2,350,724
Commercial and Industrial [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	453
Amortized Cost Basis by Origination Year 2019	2,726
Amortized Cost Basis by Origination Year 2018	4,206
Amortized Cost Basis by Origination Year 2017	2,795
Amortized Cost Basis by Origination Year 2016	324
Amortized Cost Basis by Origination Year, Prior to 2016	11,640
Revolving Loans	12,453
Portfolio loans, net of unearned income	34,597
Commercial and Industrial [Member] | Classified - substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019	3,817
Amortized Cost Basis by Origination Year 2018	1,947
Amortized Cost Basis by Origination Year 2017	3,771
Amortized Cost Basis by Origination Year 2016	1,603
Amortized Cost Basis by Origination Year, Prior to 2016	5,073
Revolving Loans	5,906
Portfolio loans, net of unearned income	$ 22,117