Loans and Allowance for Credit Losses - Schedule of Risk Rating and Payment Performance (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	$ 12,384,612	$ 12,117,524	$ 12,117,524
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	77,746
Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	3,792
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,701
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	362,653
2016	190,051
2017	380,753
2018	339,179
2019	562,140
2020	216,352
Revolving Loans	643,218
Revolving to Term Loans	150,119
Total loans and leases outstanding	2,844,465	2,815,154	2,890,296
Commercial | Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			713,092
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	6,802
Commercial | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	396
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,522
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	848,830
2016	641,326
2017	941,628
2018	902,976
2019	1,176,472
2020	280,380
Revolving Loans	26,186
Revolving to Term Loans	300,641
Total loans and leases outstanding	5,118,439	4,889,253	5,166,792
Commercial real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	40,361
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	179
BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	18,130
2016	32,928
2017	47,825
2018	63,508
2019	93,728
2020	26,287
Revolving Loans	62,804
Revolving to Term Loans	21,929
Total loans and leases outstanding	367,139	352,681
BBCC | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	1,930
BBCC | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	246
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	847,460
2016	293,954
2017	304,424
2018	220,075
2019	561,419
2020	100,385
Revolving Loans	0
Revolving to Term Loans	134
Total loans and leases outstanding	2,327,851	2,334,289	2,334,289
Residential real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	23,567		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	826,831
2016	292,199
2017	303,763
2018	219,650
2019	561,322
2020	100,385
Revolving Loans	0
Revolving to Term Loans	134
Total loans and leases outstanding	2,304,284		2,311,670
Residential real estate | Performing | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			555,025
Residential real estate | Performing | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			1,013,760
Residential real estate | Performing | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			147,383
Residential real estate | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	20,629
2016	1,755
2017	661
2018	425
2019	97
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	23,567		22,619
Residential real estate | Nonperforming | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			3,996
Residential real estate | Nonperforming | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			3,527
Residential real estate | Nonperforming | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			2,456
Indirect
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	53,333
2016	100,600
2017	153,995
2018	199,779
2019	349,107
2020	96,230
Revolving Loans	0
Revolving to Term Loans	92
Total loans and leases outstanding	953,136	935,584
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	2,885
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	53,056
2016	99,915
2017	152,882
2018	199,211
2019	348,865
2020	96,230
Revolving Loans	0
Revolving to Term Loans	92
Total loans and leases outstanding	950,251
Indirect | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	277
2016	685
2017	1,113
2018	568
2019	242
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	2,885
Direct
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	30,342
2016	15,694
2017	28,515
2018	48,801
2019	46,653
2020	12,485
Revolving Loans	27,834
Revolving to Term Loans	1,469
Total loans and leases outstanding	211,793	228,524
Direct | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	863
Direct | Auto
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	265
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	29,807
2016	15,445
2017	28,370
2018	48,587
2019	46,602
2020	12,485
Revolving Loans	27,834
Revolving to Term Loans	1,468
Total loans and leases outstanding	210,598
Direct | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	535
2016	249
2017	145
2018	214
2019	51
2020	0
Revolving Loans	0
Revolving to Term Loans	1
Total loans and leases outstanding	1,195
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	566
2017	1,039
2018	719
2019	1,116
2020	0
Revolving Loans	535,284
Revolving to Term Loans	23,065
Total loans and leases outstanding	561,789	$ 562,039
Home equity | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding	4,223
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	240
2017	1,002
2018	719
2019	1,085
2020	0
Revolving Loans	535,095
Revolving to Term Loans	19,425
Total loans and leases outstanding	557,566
Home equity | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	326
2017	37
2018	0
2019	31
2020	0
Revolving Loans	189
Revolving to Term Loans	3,640
Total loans and leases outstanding	4,223
Pass | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	339,465
2016	177,397
2017	342,542
2018	312,229
2019	546,484
2020	213,893
Revolving Loans	581,830
Revolving to Term Loans	138,584
Total loans and leases outstanding	2,652,424		2,702,605
Pass | Commercial | Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			665,512
Pass | Commercial | Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			4,191,455
Pass | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	793,743
2016	596,312
2017	838,575
2018	864,477
2019	1,149,445
2020	280,341
Revolving Loans	25,474
Revolving to Term Loans	282,936
Total loans and leases outstanding	4,831,303
Pass | BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	17,943
2016	30,762
2017	45,700
2018	61,865
2019	90,970
2020	26,069
Revolving Loans	58,040
Revolving to Term Loans	18,679
Total loans and leases outstanding	350,028
Criticized | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	9,386
2016	6,799
2017	12,704
2018	12,995
2019	4,707
2020	1,708
Revolving Loans	39,157
Revolving to Term Loans	1,356
Total loans and leases outstanding	88,812		84,676
Criticized | Commercial | Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			34,651
Criticized | Commercial | Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			115,514
Criticized | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	22,910
2016	12,915
2017	69,842
2018	7,933
2019	20,007
2020	0
Revolving Loans	500
Revolving to Term Loans	6,522
Total loans and leases outstanding	140,629
Criticized | BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	1,024
2017	522
2018	512
2019	877
2020	172
Revolving Loans	4,044
Revolving to Term Loans	1,419
Total loans and leases outstanding	8,570
Classified - substandard | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	9,935
2016	4,268
2017	13,345
2018	7,893
2019	5,421
2020	751
Revolving Loans	18,326
Revolving to Term Loans	3,397
Total loans and leases outstanding	63,336		63,979
Classified - substandard | Commercial | Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			0
Classified - substandard | Commercial | Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			101,693
Classified - substandard | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	12,944
2016	17,519
2017	27,025
2018	23,741
2019	2,878
2020	39
Revolving Loans	212
Revolving to Term Loans	10,792
Total loans and leases outstanding	95,150
Classified - substandard | BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	551
2017	1,028
2018	0
2019	1,443
2020	0
Revolving Loans	644
Revolving to Term Loans	1,008
Total loans and leases outstanding	4,674
Classified - nonaccrual | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	816
2016	784
2017	2,324
2018	5,905
2019	3,274
2020	0
Revolving Loans	3,905
Revolving to Term Loans	6,782
Total loans and leases outstanding	23,790		22,240
Classified - nonaccrual | Commercial | Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			12,929
Classified - nonaccrual | Commercial | Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			38,822
Classified - nonaccrual | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	15,352
2016	14,368
2017	1,830
2018	3,525
2019	2,177
2020	0
Revolving Loans	0
Revolving to Term Loans	391
Total loans and leases outstanding	37,643
Classified - nonaccrual | BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	0
2016	538
2017	575
2018	1,070
2019	438
2020	46
Revolving Loans	76
Revolving to Term Loans	823
Total loans and leases outstanding	3,566
Classified - doubtful | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	3,051
2016	803
2017	9,838
2018	157
2019	2,254
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	16,103		16,796
Classified - doubtful | Commercial | Real Estate - Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			0
Classified - doubtful | Commercial | Real Estate - Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases outstanding			$ 6,216
Classified - doubtful | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	3,881
2016	212
2017	4,356
2018	3,300
2019	1,965
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	13,714
Classified - doubtful | BBCC
Financing Receivable, Credit Quality Indicator [Line Items]
Prior to 2016	187
2016	53
2017	0
2018	61
2019	0
2020	0
Revolving Loans	0
Revolving to Term Loans	0
Total loans and leases outstanding	$ 301