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	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 10,357,192		$ 10,789,233
Current-period gross write-offs	(3,557)	$ (9,011)
Current-period recoveries	3,598	2,353
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,567		16,856
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,276		16,051
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,862		35,242
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	14,307		18,315
Amortized Cost Basis by Origination Year 2020	8,093		3,611
Amortized Cost Basis by Origination Year 2019	2,796		3,376
Amortized Cost Basis by Origination Year 2018	2,595		1,131
Amortized Cost Basis by Origination Year 2017	917		1,198
Amortized Cost Basis by Origination Year, Prior to 2017	17,971		19,159
Revolving Loans	573,168		586,557
Revolving Loans Converted to Term	11,212		13,040
Total loans	631,059		646,387
Current-period gross write-offs	(274)	(562)
Current-period recoveries	340	255
Home Equity [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	14,307		18,191
Amortized Cost Basis by Origination Year 2020	8,093		3,611
Amortized Cost Basis by Origination Year 2019	2,796		3,334
Amortized Cost Basis by Origination Year 2018	2,560		975
Amortized Cost Basis by Origination Year 2017	756		1,110
Amortized Cost Basis by Origination Year, Prior to 2017	15,620		16,477
Revolving Loans	570,646		583,486
Revolving Loans Converted to Term	10,395		12,135
Total loans	625,173		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 2018	12
Amortized Cost Basis by Origination Year 2017	11
Amortized Cost Basis by Origination Year, Prior to 2017	583		882
Revolving Loans	1,398		1,247
Revolving Loans Converted to Term	131		127
Total loans	2,135		2,414
Home Equity [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2018	16
Amortized Cost Basis by Origination Year, Prior to 2017	243		14
Revolving Loans	158		749
Revolving Loans Converted to Term			12
Total loans	417		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	7		156
Amortized Cost Basis by Origination Year 2017	150		88
Amortized Cost Basis by Origination Year, Prior to 2017	1,525		1,786
Revolving Loans	966		1,075
Revolving Loans Converted to Term	686		766
Total loans	3,334		3,879
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,705,246		5,705,392
Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,666		5,458
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,855		6,394
Commercial Real Estate [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,338		11,738
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	201,823		385,541
Amortized Cost Basis by Origination Year 2020	386,437		243,253
Amortized Cost Basis by Origination Year 2019	181,835		150,912
Amortized Cost Basis by Origination Year 2018	106,118		109,384
Amortized Cost Basis by Origination Year 2017	82,725		171,971
Amortized Cost Basis by Origination Year, Prior to 2017	666,694		659,900
Total loans	1,625,632		1,720,961
Current-period gross write-offs	(441)	(667)
Current-period recoveries	742	376
Residential Real Estate [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	201,823		385,541
Amortized Cost Basis by Origination Year 2020	386,437		242,770
Amortized Cost Basis by Origination Year 2019	181,367		149,603
Amortized Cost Basis by Origination Year 2018	105,727		108,090
Amortized Cost Basis by Origination Year 2017	81,964		170,967
Amortized Cost Basis by Origination Year, Prior to 2017	653,290		641,665
Total loans	1,610,608		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			533
Amortized Cost Basis by Origination Year, Prior to 2017	1,153		1,761
Total loans	1,153		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	123
Amortized Cost Basis by Origination Year 2017			185
Amortized Cost Basis by Origination Year, Prior to 2017	2,137		4,646
Total loans	2,260		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	468		166
Amortized Cost Basis by Origination Year 2018	268		761
Amortized Cost Basis by Origination Year 2017	761		819
Amortized Cost Basis by Origination Year, Prior to 2017	10,114		11,828
Total loans	11,611		14,057
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	36,891		73,714
Amortized Cost Basis by Origination Year 2020	59,353		90,264
Amortized Cost Basis by Origination Year 2019	68,210		39,951
Amortized Cost Basis by Origination Year 2018	28,878		22,560
Amortized Cost Basis by Origination Year 2017	15,756		13,513
Amortized Cost Basis by Origination Year, Prior to 2017	43,894		46,609
Revolving Loans	22,888		22,279
Revolving Loans Converted to Term	199		165
Total loans	276,069		309,055
Current-period gross write-offs	(1,406)	(2,183)
Current-period recoveries	1,042	768
Consumer [Member] | Current [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	36,753		72,847
Amortized Cost Basis by Origination Year 2020	58,550		89,637
Amortized Cost Basis by Origination Year 2019	67,642		39,584
Amortized Cost Basis by Origination Year 2018	28,608		22,118
Amortized Cost Basis by Origination Year 2017	15,557		13,144
Amortized Cost Basis by Origination Year, Prior to 2017	43,311		45,735
Revolving Loans	22,817		22,253
Revolving Loans Converted to Term	199		165
Total loans	273,437		305,483
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	132		481
Amortized Cost Basis by Origination Year 2020	496		408
Amortized Cost Basis by Origination Year 2019	353		210
Amortized Cost Basis by Origination Year 2018	183		311
Amortized Cost Basis by Origination Year 2017	102		194
Amortized Cost Basis by Origination Year, Prior to 2017	324		379
Revolving Loans	59		15
Total loans	1,649		1,998
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	6		273
Amortized Cost Basis by Origination Year 2020	201		147
Amortized Cost Basis by Origination Year 2019	163		84
Amortized Cost Basis by Origination Year 2018	66		100
Amortized Cost Basis by Origination Year 2017	89		163
Amortized Cost Basis by Origination Year, Prior to 2017	121		253
Revolving Loans	2		11
Total loans	648		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	106		72
Amortized Cost Basis by Origination Year 2019	52		73
Amortized Cost Basis by Origination Year 2018	21		31
Amortized Cost Basis by Origination Year 2017	8		12
Amortized Cost Basis by Origination Year, Prior to 2017	138		242
Revolving Loans	10
Total loans	335		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	73,210		134,179
Amortized Cost Basis by Origination Year 2020	153,508		314,614
Amortized Cost Basis by Origination Year 2019	229,044		111,167
Amortized Cost Basis by Origination Year 2018	37,933		27,774
Amortized Cost Basis by Origination Year 2017	25,776		16,774
Amortized Cost Basis by Origination Year, Prior to 2017	43,437		36,156
Revolving Loans	25,310		27,613
Total loans	588,218		668,277
Current-period gross write-offs	(22)	(1)
Current-period recoveries	110	77
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,149		582
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans			2,276
Commercial Real Estate - Land and Construction [Member] | Commercial Real Estate [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	157		429
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	73,210		133,720
Amortized Cost Basis by Origination Year 2020	152,277		314,614
Amortized Cost Basis by Origination Year 2019	229,044		109,232
Amortized Cost Basis by Origination Year 2018	37,823		27,483
Amortized Cost Basis by Origination Year 2017	25,554		16,404
Amortized Cost Basis by Origination Year, Prior to 2017	39,097		29,685
Revolving Loans	24,592		26,297
Total loans	581,597		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	1,231
Amortized Cost Basis by Origination Year 2019			1,532
Amortized Cost Basis by Origination Year 2018	36		233
Amortized Cost Basis by Origination Year 2017	222		79
Amortized Cost Basis by Origination Year, Prior to 2017	2,783		3,778
Revolving Loans	718		1,316
Total loans	4,990		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			291
Amortized Cost Basis by Origination Year, Prior to 2017	1,557		2,693
Total loans	1,631		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	368,546		812,311
Amortized Cost Basis by Origination Year 2020	807,900		754,181
Amortized Cost Basis by Origination Year 2019	790,864		668,368
Amortized Cost Basis by Origination Year 2018	635,735		545,520
Amortized Cost Basis by Origination Year 2017	495,078		633,477
Amortized Cost Basis by Origination Year, Prior to 2017	1,951,492		1,532,366
Revolving Loans	67,413		90,892
Total loans	5,117,028		5,037,115
Current-period gross write-offs	(235)	(1,895)
Current-period recoveries	646	396
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,517		4,876
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,855		4,118
Commercial Real Estate - Improved Property [Member] | Commercial Real Estate [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,181		11,309
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	368,546		809,516
Amortized Cost Basis by Origination Year 2020	798,091		670,554
Amortized Cost Basis by Origination Year 2019	687,356		646,629
Amortized Cost Basis by Origination Year 2018	600,389		474,622
Amortized Cost Basis by Origination Year 2017	441,913		572,733
Amortized Cost Basis by Origination Year, Prior to 2017	1,770,502		1,346,552
Revolving Loans	66,697		89,120
Total loans	4,733,494		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	8,334		67,261
Amortized Cost Basis by Origination Year 2019	95,233		16,793
Amortized Cost Basis by Origination Year 2018	31,599		59,251
Amortized Cost Basis by Origination Year 2017	46,679		42,284
Amortized Cost Basis by Origination Year, Prior to 2017	101,682		130,247
Revolving Loans	716		1,772
Total loans	284,243		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	1,475		16,366
Amortized Cost Basis by Origination Year 2019	8,275		4,946
Amortized Cost Basis by Origination Year 2018	3,747		11,647
Amortized Cost Basis by Origination Year 2017	6,486		18,460
Amortized Cost Basis by Origination Year, Prior to 2017	79,308		55,567
Total loans	99,291		107,088
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	479,472		977,538
Amortized Cost Basis by Origination Year 2020	397,058		246,805
Amortized Cost Basis by Origination Year 2019	190,539		199,865
Amortized Cost Basis by Origination Year 2018	184,856		167,490
Amortized Cost Basis by Origination Year 2017	132,197		87,306
Amortized Cost Basis by Origination Year, Prior to 2017	316,919		282,603
Revolving Loans	418,021		445,695
Revolving Loans Converted to Term	124		136
Total loans	2,119,186		2,407,438
Current-period gross write-offs	(814)	(3,187)
Current-period recoveries	518	$ 227
Commercial and Industrial [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,964		4,372
Commercial and Industrial [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,096		2,197
Commercial and Industrial [Member] | 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,244		5,025
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	479,447		977,085
Amortized Cost Basis by Origination Year 2020	392,500		240,262
Amortized Cost Basis by Origination Year 2019	165,745		193,712
Amortized Cost Basis by Origination Year 2018	180,175		160,924
Amortized Cost Basis by Origination Year 2017	127,825		85,379
Amortized Cost Basis by Origination Year, Prior to 2017	305,290		265,890
Revolving Loans	401,860		427,336
Revolving Loans Converted to Term	124		136
Total loans	2,052,966		2,350,724
Commercial and Industrial [Member] | Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2021	25		453
Amortized Cost Basis by Origination Year 2020	3,875		2,726
Amortized Cost Basis by Origination Year 2019	1,805		4,206
Amortized Cost Basis by Origination Year 2018	3,026		2,795
Amortized Cost Basis by Origination Year 2017	2,572		324
Amortized Cost Basis by Origination Year, Prior to 2017	6,689		11,640
Revolving Loans	12,223		12,453
Total loans	30,215		34,597
Commercial and Industrial [Member] | Classified - substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost Basis by Origination Year 2020	683		3,817
Amortized Cost Basis by Origination Year 2019	22,989		1,947
Amortized Cost Basis by Origination Year 2018	1,655		3,771
Amortized Cost Basis by Origination Year 2017	1,800		1,603
Amortized Cost Basis by Origination Year, Prior to 2017	4,940		5,073
Revolving Loans	3,938		5,906
Total loans	$ 36,005		$ 22,117