Loans and Allowance for Credit Losses - Schedule of Risk Rating and Payment Performance (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	$ 13,615,701	$ 12,117,524	$ 12,117,524
Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	13,615,701	12,122,002
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	78,547
Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	3,736
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,267
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	4,307,505	2,815,154	2,890,296
Commercial | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	334,720
2016	175,780
2017	353,979
2018	313,421
2019	556,384
2020	1,687,329
Revolving Loans	538,577
Revolving to Term Loans	153,454
Total loans and leases outstanding	4,113,644	2,817,833
Commercial | Commercial Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			713,092
Commercial | Commercial Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			4,453,700
Commercial | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	9,143
Commercial | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	456
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,107
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	5,403,316	4,889,253	5,166,792
Commercial real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	749,720
2016	608,402
2017	869,773
2018	886,186
2019	1,076,569
2020	682,336
Revolving Loans	27,954
Revolving to Term Loans	336,007
Total loans and leases outstanding	5,236,947	4,890,890
Commercial real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	38,065
Commercial real estate | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Commercial real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	160
BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding		352,681
BBCC | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	12,231
2016	29,882
2017	43,867
2018	60,319
2019	90,299
2020	46,294
Revolving Loans	51,699
Revolving to Term Loans	25,639
Total loans and leases outstanding	360,230	352,714
BBCC | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,836
BBCC | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	190
BBCC | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	804,375
2016	260,365
2017	263,866
2018	183,006
2019	532,509
2020	185,047
Revolving Loans	0
Revolving to Term Loans	130
Total loans and leases outstanding	2,229,298	2,334,289	2,334,289
Residential real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	2,229,298	2,334,394
Residential real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	24,315		559,021
Residential real estate | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0		1,017,287
Residential real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0		149,839
Residential real estate | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	783,682
2016	258,164
2017	263,238
2018	182,395
2019	532,392
2020	184,982
Revolving Loans	0
Revolving to Term Loans	130
Total loans and leases outstanding	2,204,983		2,311,670
Residential real estate | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	20,693
2016	2,201
2017	628
2018	611
2019	117
2020	65
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	24,315		22,619
Indirect
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	40,025
2016	82,898
2017	134,566
2018	177,560
2019	317,801
2020	180,779
Revolving Loans	0
Revolving to Term Loans	94
Total loans and leases outstanding	933,723	935,584
Indirect | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	933,723	935,594
Indirect | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Indirect | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	2,835
Indirect | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Indirect | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	39,794
2016	82,247
2017	133,548
2018	176,931
2019	317,495
2020	180,779
Revolving Loans	0
Revolving to Term Loans	94
Total loans and leases outstanding	930,888
Indirect | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	231
2016	651
2017	1,018
2018	629
2019	306
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	2,835
Direct
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	25,890
2016	13,229
2017	24,151
2018	42,144
2019	39,477
2020	21,258
Revolving Loans	26,350
Revolving to Term Loans	2,074
Total loans and leases outstanding	194,573	228,524
Direct | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	194,573	228,526
Direct | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	862
Direct | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	255
Direct | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Direct | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	25,369
2016	12,951
2017	24,025
2018	41,987
2019	39,424
2020	21,258
Revolving Loans	26,350
Revolving to Term Loans	2,072
Total loans and leases outstanding	193,436
Direct | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	521
2016	278
2017	126
2018	157
2019	53
2020	0
Revolving Loans	0
Revolving to Term Loans	2
Total loans and leases outstanding	1,137
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	661
2017	1,104
2018	990
2019	1,146
2020	0
Revolving Loans	519,746
Revolving to Term Loans	23,639
Total loans and leases outstanding	547,286	562,039
Home equity | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	547,286	$ 562,051
Home equity | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	4,326
Home equity | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Home equity | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	0
Home equity | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	436
2017	1,067
2018	990
2019	1,116
2020	0
Revolving Loans	519,472
Revolving to Term Loans	19,878
Total loans and leases outstanding	542,959
Home equity | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	225
2017	37
2018	0
2019	30
2020	0
Revolving Loans	274
Revolving to Term Loans	3,761
Total loans and leases outstanding	4,327
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,675,582		1,726,147
Consumer | Performing | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			1,013,760
Consumer | Performing | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			147,383
Consumer | Performing | Home Equity Line of Credit
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			555,025
Consumer | Nonperforming | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			3,527
Consumer | Nonperforming | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			2,456
Consumer | Nonperforming | Home Equity Line of Credit
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			3,996
Pass | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			2,702,605
Pass | Commercial | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	315,486
2016	164,951
2017	315,876
2018	279,110
2019	537,539
2020	1,683,849
Revolving Loans	502,947
Revolving to Term Loans	137,905
Total loans and leases outstanding	3,937,663
Pass | Commercial | Commercial Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			665,512
Pass | Commercial | Commercial Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			4,191,455
Pass | Commercial real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	696,386
2016	568,658
2017	769,069
2018	851,522
2019	1,030,103
2020	678,684
Revolving Loans	27,710
Revolving to Term Loans	318,622
Total loans and leases outstanding	4,940,754
Pass | BBCC | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	12,140
2016	28,945
2017	42,552
2018	58,668
2019	87,160
2020	44,309
Revolving Loans	48,419
Revolving to Term Loans	21,631
Total loans and leases outstanding	343,824
Criticized | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			84,676
Criticized | Commercial | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	8,196
2016	4,737
2017	8,898
2018	16,801
2019	8,710
2020	2,347
Revolving Loans	19,101
Revolving to Term Loans	2,622
Total loans and leases outstanding	71,412
Criticized | Commercial | Commercial Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			34,651
Criticized | Commercial | Commercial Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			115,514
Criticized | Commercial real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	17,734
2016	7,647
2017	53,841
2018	12,341
2019	39,620
2020	2,326
Revolving Loans	0
Revolving to Term Loans	6,370
Total loans and leases outstanding	139,879
Criticized | BBCC | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	765
2017	639
2018	768
2019	1,411
2020	1,061
Revolving Loans	2,685
Revolving to Term Loans	1,682
Total loans and leases outstanding	9,011
Classified - Substandard | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			63,979
Classified - Substandard | Commercial | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	6,818
2016	4,641
2017	16,141
2018	11,808
2019	5,960
2020	1,133
Revolving Loans	13,462
Revolving to Term Loans	6,821
Total loans and leases outstanding	66,784
Classified - Substandard | Commercial | Commercial Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			0
Classified - Substandard | Commercial | Commercial Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			101,693
Classified - Substandard | Commercial real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	17,006
2016	19,770
2017	38,710
2018	14,757
2019	2,754
2020	1,326
Revolving Loans	244
Revolving to Term Loans	10,647
Total loans and leases outstanding	105,214
Classified - Substandard | BBCC | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	52
2017	196
2018	39
2019	1,199
2020	232
Revolving Loans	520
Revolving to Term Loans	1,110
Total loans and leases outstanding	3,348
Classified - Nonaccrual | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			22,240
Classified - Nonaccrual | Commercial | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	2,474
2016	832
2017	4,139
2018	5,219
2019	4,175
2020	0
Revolving Loans	3,067
Revolving to Term Loans	6,106
Total loans and leases outstanding	26,012
Classified - Nonaccrual | Commercial | Commercial Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			12,929
Classified - Nonaccrual | Commercial | Commercial Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			38,822
Classified - Nonaccrual | Commercial real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	15,380
2016	2,362
2017	3,886
2018	4,310
2019	2,172
2020	0
Revolving Loans	0
Revolving to Term Loans	368
Total loans and leases outstanding	28,478
Classified - Nonaccrual | BBCC | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	120
2017	408
2018	380
2019	529
2020	692
Revolving Loans	75
Revolving to Term Loans	1,216
Total loans and leases outstanding	3,420
Classified - Doubtful | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			16,796
Classified - Doubtful | Commercial | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	1,746
2016	619
2017	8,925
2018	483
2019	0
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	11,773
Classified - Doubtful | Commercial | Commercial Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			0
Classified - Doubtful | Commercial | Commercial Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			$ 6,216
Classified - Doubtful | Commercial real estate | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	3,214
2016	9,965
2017	4,267
2018	3,256
2019	1,920
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	22,622
Classified - Doubtful | BBCC | Adjusted Balance
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	91
2016	0
2017	72
2018	464
2019	0
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	$ 627