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, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Portfolio loans, net of unearned income	$ 10,703,312		$ 10,789,233
Current-period gross write-offs	(2,460)	$ (6,126)
Current-period recoveries	1,812	1,410
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	4,724		18,315
Amortized Cost Basis by Origination Year 2020	15,055		3,611
Amortized Cost Basis by Origination Year 2019	3,290		3,376
Amortized Cost Basis by Origination Year 2018	2,978		1,131
Amortized Cost Basis by Origination Year 2017	1,007		1,198
Amortized Cost Basis by Origination Year, Prior to 2017	19,081		19,159
Revolving Loans	575,867		586,557
Revolving Loans Converted to Term	12,016		13,040
Portfolio loans, net of unearned income	634,018		646,387
Current-period gross write-offs	(174)	(443)
Current-period recoveries	79	172
Home Equity [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	4,724		18,191
Amortized Cost Basis by Origination Year 2020	15,055		3,611
Amortized Cost Basis by Origination Year 2019	3,290		3,334
Amortized Cost Basis by Origination Year 2018	2,959		975
Amortized Cost Basis by Origination Year 2017	857		1,110
Amortized Cost Basis by Origination Year, Prior to 2017	16,995		16,477
Revolving Loans	573,653		583,486
Revolving Loans Converted to Term	11,240		12,135
Portfolio loans, net of unearned income	628,773		639,319
Home Equity [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021			124
Amortized Cost Basis by Origination Year 2019			34
Amortized Cost Basis by Origination Year, Prior to 2017	400		882
Revolving Loans	783		1,247
Revolving Loans Converted to Term	30		127
Portfolio loans, net of unearned income	1,213		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 2017	121		14
Revolving Loans	76		749
Revolving Loans Converted to Term			12
Portfolio loans, net of unearned income	197		775
Home Equity [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019			8
Amortized Cost Basis by Origination Year 2018	19		156
Amortized Cost Basis by Origination Year 2017	150		88
Amortized Cost Basis by Origination Year, Prior to 2017	1,565		1,786
Revolving Loans	1,355		1,075
Revolving Loans Converted to Term	746		766
Portfolio loans, net of unearned income	3,835		3,879
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Portfolio loans, net of unearned income	5,712,742		5,705,392
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	66,997		385,541
Amortized Cost Basis by Origination Year 2020	392,577		243,253
Amortized Cost Basis by Origination Year 2019	209,613		150,912
Amortized Cost Basis by Origination Year 2018	131,570		109,384
Amortized Cost Basis by Origination Year 2017	95,111		171,971
Amortized Cost Basis by Origination Year, Prior to 2017	748,554		659,900
Portfolio loans, net of unearned income	1,644,422		1,720,961
Current-period gross write-offs	(371)	(386)
Current-period recoveries	135	272
Residential Real Estate [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	66,997		385,541
Amortized Cost Basis by Origination Year 2020	392,577		242,770
Amortized Cost Basis by Origination Year 2019	209,234		149,603
Amortized Cost Basis by Origination Year 2018	130,435		108,090
Amortized Cost Basis by Origination Year 2017	94,237		170,967
Amortized Cost Basis by Origination Year, Prior to 2017	731,848		641,665
Portfolio loans, net of unearned income	1,625,328		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 2019			320
Amortized Cost Basis by Origination Year 2018	79		533
Amortized Cost Basis by Origination Year, Prior to 2017	2,634		1,761
Portfolio loans, net of unearned income	2,713		2,614
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2019			823
Amortized Cost Basis by Origination Year 2018	272
Amortized Cost Basis by Origination Year 2017	113		185
Amortized Cost Basis by Origination Year, Prior to 2017	1,204		4,646
Portfolio loans, net of unearned income	1,589		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 2020			483
Amortized Cost Basis by Origination Year 2019	379		166
Amortized Cost Basis by Origination Year 2018	784		761
Amortized Cost Basis by Origination Year 2017	761		819
Amortized Cost Basis by Origination Year, Prior to 2017	12,868		11,828
Portfolio loans, net of unearned income	14,792		14,057
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	18,158		73,714
Amortized Cost Basis by Origination Year 2020	66,299		90,264
Amortized Cost Basis by Origination Year 2019	79,508		39,951
Amortized Cost Basis by Origination Year 2018	33,739		22,560
Amortized Cost Basis by Origination Year 2017	18,980		13,513
Amortized Cost Basis by Origination Year, Prior to 2017	51,938		46,609
Revolving Loans	20,607		22,279
Revolving Loans Converted to Term	166		165
Portfolio loans, net of unearned income	289,395		309,055
Current-period gross write-offs	(927)	(856)
Current-period recoveries	462	415
Consumer [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	18,121		72,847
Amortized Cost Basis by Origination Year 2020	65,802		89,637
Amortized Cost Basis by Origination Year 2019	79,045		39,584
Amortized Cost Basis by Origination Year 2018	33,586		22,118
Amortized Cost Basis by Origination Year 2017	18,773		13,144
Amortized Cost Basis by Origination Year, Prior to 2017	51,313		45,735
Revolving Loans	20,589		22,253
Revolving Loans Converted to Term	166		165
Portfolio loans, net of unearned income	287,395		305,483
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	37		481
Amortized Cost Basis by Origination Year 2020	444		408
Amortized Cost Basis by Origination Year 2019	413		210
Amortized Cost Basis by Origination Year 2018	68		311
Amortized Cost Basis by Origination Year 2017	114		194
Amortized Cost Basis by Origination Year, Prior to 2017	352		379
Revolving Loans			15
Portfolio loans, net of unearned income	1,428		1,998
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021			273
Amortized Cost Basis by Origination Year 2020	45		147
Amortized Cost Basis by Origination Year 2019	50		84
Amortized Cost Basis by Origination Year 2018	31		100
Amortized Cost Basis by Origination Year 2017	64		163
Amortized Cost Basis by Origination Year, Prior to 2017	148		253
Revolving Loans	2		11
Portfolio loans, net of unearned income	340		1,031
Consumer [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021			113
Amortized Cost Basis by Origination Year 2020	8		72
Amortized Cost Basis by Origination Year 2019			73
Amortized Cost Basis by Origination Year 2018	54		31
Amortized Cost Basis by Origination Year 2017	29		12
Amortized Cost Basis by Origination Year, Prior to 2017	125		242
Revolving Loans	16
Portfolio loans, net of unearned income	232		543
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	30,840		134,179
Amortized Cost Basis by Origination Year 2020	165,814		314,614
Amortized Cost Basis by Origination Year 2019	296,600		111,167
Amortized Cost Basis by Origination Year 2018	49,862		27,774
Amortized Cost Basis by Origination Year 2017	27,332		16,774
Amortized Cost Basis by Origination Year, Prior to 2017	48,469		36,156
Revolving Loans	23,100		27,613
Portfolio loans, net of unearned income	642,017		668,277
Current-period gross write-offs	(18)	(1)
Current-period recoveries	55	8
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 2021	30,840		133,720
Amortized Cost Basis by Origination Year 2020	164,939		314,614
Amortized Cost Basis by Origination Year 2019	296,600		109,232
Amortized Cost Basis by Origination Year 2018	49,749		27,483
Amortized Cost Basis by Origination Year 2017	27,064		16,404
Amortized Cost Basis by Origination Year, Prior to 2017	43,143		29,685
Revolving Loans	22,500		26,297
Portfolio loans, net of unearned income	634,835		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 2021			459
Amortized Cost Basis by Origination Year 2020	875
Amortized Cost Basis by Origination Year 2019			1,532
Amortized Cost Basis by Origination Year 2018	39		233
Amortized Cost Basis by Origination Year 2017	228		79
Amortized Cost Basis by Origination Year, Prior to 2017	3,618		3,778
Revolving Loans	600		1,316
Portfolio loans, net of unearned income	5,360		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 2019			403
Amortized Cost Basis by Origination Year 2018	74		58
Amortized Cost Basis by Origination Year 2017	40		291
Amortized Cost Basis by Origination Year, Prior to 2017	1,708		2,693
Portfolio loans, net of unearned income	1,822		3,445
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	156,789		812,311
Amortized Cost Basis by Origination Year 2020	789,410		754,181
Amortized Cost Basis by Origination Year 2019	772,808		668,368
Amortized Cost Basis by Origination Year 2018	659,248		545,520
Amortized Cost Basis by Origination Year 2017	533,548		633,477
Amortized Cost Basis by Origination Year, Prior to 2017	2,071,424		1,532,366
Revolving Loans	87,498		90,892
Portfolio loans, net of unearned income	5,070,725		5,037,115
Current-period gross write-offs	(19)	(1,398)
Current-period recoveries	528	293
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	156,789		809,516
Amortized Cost Basis by Origination Year 2020	787,296		670,554
Amortized Cost Basis by Origination Year 2019	690,398		646,629
Amortized Cost Basis by Origination Year 2018	639,915		474,622
Amortized Cost Basis by Origination Year 2017	472,801		572,733
Amortized Cost Basis by Origination Year, Prior to 2017	1,864,909		1,346,552
Revolving Loans	67,149		89,120
Portfolio loans, net of unearned income	4,679,257		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 2021			2,693
Amortized Cost Basis by Origination Year 2020	1,892		67,261
Amortized Cost Basis by Origination Year 2019	53,807		16,793
Amortized Cost Basis by Origination Year 2018	17,473		59,251
Amortized Cost Basis by Origination Year 2017	53,576		42,284
Amortized Cost Basis by Origination Year, Prior to 2017	150,704		130,247
Revolving Loans	20,349		1,772
Portfolio loans, net of unearned income	297,801		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 2021			102
Amortized Cost Basis by Origination Year 2020	222		16,366
Amortized Cost Basis by Origination Year 2019	28,603		4,946
Amortized Cost Basis by Origination Year 2018	1,860		11,647
Amortized Cost Basis by Origination Year 2017	7,171		18,460
Amortized Cost Basis by Origination Year, Prior to 2017	55,811		55,567
Portfolio loans, net of unearned income	93,667		107,088
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	402,334		977,538
Amortized Cost Basis by Origination Year 2020	688,922		246,805
Amortized Cost Basis by Origination Year 2019	237,586		199,865
Amortized Cost Basis by Origination Year 2018	191,388		167,490
Amortized Cost Basis by Origination Year 2017	142,074		87,306
Amortized Cost Basis by Origination Year, Prior to 2017	336,808		282,603
Revolving Loans	423,493		445,695
Revolving Loans Converted to Term	130		136
Portfolio loans, net of unearned income	2,422,735		2,407,438
Current-period gross write-offs	(750)	(2,714)
Current-period recoveries	440	$ 107
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	401,323		977,085
Amortized Cost Basis by Origination Year 2020	685,632		240,262
Amortized Cost Basis by Origination Year 2019	232,322		193,712
Amortized Cost Basis by Origination Year 2018	185,484		160,924
Amortized Cost Basis by Origination Year 2017	135,856		85,379
Amortized Cost Basis by Origination Year, Prior to 2017	320,788		265,890
Revolving Loans	404,023		427,336
Revolving Loans Converted to Term	130		136
Portfolio loans, net of unearned income	2,365,558		2,350,724
Commercial and Industrial [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	26		453
Amortized Cost Basis by Origination Year 2020	3,290		2,726
Amortized Cost Basis by Origination Year 2019	2,746		4,206
Amortized Cost Basis by Origination Year 2018	4,236		2,795
Amortized Cost Basis by Origination Year 2017	2,651		324
Amortized Cost Basis by Origination Year, Prior to 2017	10,841		11,640
Revolving Loans	13,992		12,453
Portfolio loans, net of unearned income	37,782		34,597
Commercial and Industrial [Member] | Classified - substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	985
Amortized Cost Basis by Origination Year 2020			3,817
Amortized Cost Basis by Origination Year 2019	2,518		1,947
Amortized Cost Basis by Origination Year 2018	1,668		3,771
Amortized Cost Basis by Origination Year 2017	3,567		1,603
Amortized Cost Basis by Origination Year, Prior to 2017	5,179		5,073
Revolving Loans	5,478		5,906
Portfolio loans, net of unearned income	$ 19,395		$ 22,117