Credit Quality - Schedule of Risk Category of Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 10,743,055	$ 7,452,649
Owner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	109,615
2019	164,394
2018	140,250
2017	247,544
2016	311,401
Prior	625,999
Revolving loans amortized cost basis	24,940
Revolving loans converted to term loans	617
Total	1,624,760	1,201,652
Owner-Occupied [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	107,784
2019	163,097
2018	133,255
2017	244,528
2016	304,759
Prior	565,627
Revolving loans amortized cost basis	23,576
Revolving loans converted to term loans	0
Total	1,542,626
Owner-Occupied [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	1,225
2018	6,995
2017	781
2016	2,100
Prior	9,634
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	468
Total	21,203
Owner-Occupied [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	1,831
2019	72
2018	0
2017	2,235
2016	4,542
Prior	50,394
Revolving loans amortized cost basis	1,364
Revolving loans converted to term loans	149
Total	60,587
Owner-Occupied [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	344
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	344
Owner-Occupied [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	(535)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(535)
Owner-Occupied [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	310
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	310
Owner-Occupied [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	(225)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(225)
Nonowner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	297,547
2019	750,208
2018	693,846
2017	623,207
2016	606,699
Prior	1,915,793
Revolving loans amortized cost basis	115,345
Revolving loans converted to term loans	2,145
Total	5,004,790	$ 3,965,960
Nonowner-Occupied [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	297,474
2019	748,897
2018	685,228
2017	620,528
2016	582,809
Prior	1,844,405
Revolving loans amortized cost basis	115,345
Revolving loans converted to term loans	2,145
Total	4,896,831
Nonowner-Occupied [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	347
2018	0
2017	977
2016	10,645
Prior	27,024
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	38,993
Nonowner-Occupied [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	73
2019	964
2018	8,618
2017	1,702
2016	13,245
Prior	44,364
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	68,966
Nonowner-Occupied [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	0
Nonowner-Occupied [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	(690)
Prior	(1,247)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(1,937)
Nonowner-Occupied [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	722
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	722
Nonowner-Occupied [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	(690)
Prior	(525)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(1,215)
Other Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	1,509,343
2019	452,782
2018	215,946
2017	155,166
2016	161,977
Prior	380,052
Revolving loans amortized cost basis	1,234,341
Revolving loans converted to term loans	3,898
Total	4,113,505
Other Commercial Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	1,509,244
2019	451,574
2018	212,881
2017	150,587
2016	150,389
Prior	311,422
Revolving loans amortized cost basis	1,213,494
Revolving loans converted to term loans	3,071
Total	4,002,662
Other Commercial Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	99
2019	313
2018	430
2017	2,044
2016	202
Prior	20,072
Revolving loans amortized cost basis	4,053
Revolving loans converted to term loans	423
Total	27,636
Other Commercial Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	895
2018	2,635
2017	2,535
2016	11,386
Prior	48,486
Revolving loans amortized cost basis	16,794
Revolving loans converted to term loans	404
Total	83,135
Other Commercial Loans [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	72
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	72
Other Commercial Loans [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	(11)
2018	(964)
2017	(365)
2016	(6)
Prior	(5,682)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(7,028)
Other Commercial Loans [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	42
2018	16
2017	3
2016	21
Prior	332
Revolving loans amortized cost basis	32
Revolving loans converted to term loans	0
Total	446
Other Commercial Loans [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	31
2018	(948)
2017	(362)
2016	15
Prior	(5,350)
Revolving loans amortized cost basis	32
Revolving loans converted to term loans	0
Total	(6,582)
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	324,682
2019	750,541
2018	857,528
2017	397,056
2016	355,463
Prior	1,142,871
Revolving loans amortized cost basis	477,449
Revolving loans converted to term loans	4,566
Total	4,310,156
Residential Portfolio Segment [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	324,682
2019	750,044
2018	857,069
2017	393,030
2016	347,781
Prior	1,111,476
Revolving loans amortized cost basis	476,577
Revolving loans converted to term loans	4,332
Total	4,264,991
Residential Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	271
2018	0
2017	226
2016	2,349
Prior	7,014
Revolving loans amortized cost basis	435
Revolving loans converted to term loans	0
Total	10,295
Residential Portfolio Segment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	226
2018	459
2017	3,800
2016	5,333
Prior	24,252
Revolving loans amortized cost basis	437
Revolving loans converted to term loans	234
Total	34,741
Residential Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	129
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	129
Residential Portfolio Segment [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	(1)
Prior	(889)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(890)
Residential Portfolio Segment [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	101
2016	0
Prior	201
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	302
Residential Portfolio Segment [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	101
2016	(1)
Prior	(688)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(588)
Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	163,253
2019	707,077
2018	378,084
2017	173,294
2016	134,240
Prior	93,590
Revolving loans amortized cost basis	126,045
Revolving loans converted to term loans	143
Total	1,775,728
Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	163,253
2019	706,921
2018	375,025
2017	173,269
2016	133,679
Prior	70,466
Revolving loans amortized cost basis	102,752
Revolving loans converted to term loans	143
Total	1,725,510
Construction Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	1,506
2017	0
2016	561
Prior	2,681
Revolving loans amortized cost basis	995
Revolving loans converted to term loans	0
Total	5,743
Construction Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	156
2018	1,553
2017	25
2016	0
Prior	20,443
Revolving loans amortized cost basis	22,298
Revolving loans converted to term loans	0
Total	44,475
Construction Loans [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	0
Construction Loans [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	(1,969)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(1,969)
Construction Loans [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	1,361
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,361
Construction Loans [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	(608)
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	(608)
Bankcard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	8,465
Total	8,465
Bankcard [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	8,133
Total	8,133
Bankcard [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	172
Total	172
Bankcard [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	160
Total	160
Bankcard [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	0
Bankcard [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	(128)
Total	(128)
Bankcard [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	12
Total	12
Bankcard [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	(116)
Total	(116)
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	220,927
2019	494,700
2018	298,471
2017	104,779
2016	54,766
Prior	14,408
Revolving loans amortized cost basis	7,099
Revolving loans converted to term loans	0
Total	1,195,150
Other Consumer [Member] | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	220,924
2019	494,700
2018	298,460
2017	104,779
2016	54,766
Prior	14,247
Revolving loans amortized cost basis	7,095
Revolving loans converted to term loans	0
Total	1,194,971
Other Consumer [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	11
2017	0
2016	0
Prior	152
Revolving loans amortized cost basis	4
Revolving loans converted to term loans	0
Total	167
Other Consumer [Member] | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	3
2019	0
2018	0
2017	0
2016	0
Prior	9
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	12
Other Consumer [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	0
Other Consumer [Member] | YTD Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	(16)
2019	(589)
2018	(652)
2017	(272)
2016	(152)
Prior	(225)
Revolving loans amortized cost basis	(2)
Revolving loans converted to term loans	0
Total	(1,908)
Other Consumer [Member] | YTD Recoveries [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	0
2019	24
2018	33
2017	11
2016	18
Prior	124
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	210
Other Consumer [Member] | YTD Net Charge Offs [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
2020	(16)
2019	(565)
2018	(619)
2017	(261)
2016	(134)
Prior	(101)
Revolving loans amortized cost basis	(2)
Revolving loans converted to term loans	0
Total	$ (1,698)