Loans and Lease Finance Receivables and Allowance for Credit Losses - Summary of loans by type and origination year, according to our internal risk ratings (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,592,913
2019	997,198
2018	923,702
2017	942,987
2016	755,336
Prior	2,291,368
Revolving loans amortized cost basis	841,707
Revolving loans converted to term loans	57,323
Total	8,402,534	$ 7,568,319
Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	62,537
2019	167,301
2018	82,214
2017	70,327
2016	44,756
Prior	83,714
Revolving loans amortized cost basis	317,927
Revolving loans converted to term loans	11,962
Total	840,738
Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26,248
2019	13,448
2018	48,021
2017	79,800
2016	30,213
Prior	102,426
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	300,156
SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,097,150
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,097,150
Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	368,684
2019	728,087
2018	733,361
2017	727,361
2016	620,130
Prior	1,972,501
Revolving loans amortized cost basis	193,891
Revolving loans converted to term loans	21,105
Total	5,365,120
Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,259
2019	16,733
2018	17,013
2017	17,780
2016	10,592
Prior	5
Revolving loans amortized cost basis	52,949
Revolving loans converted to term loans	5,484
Total	125,815
Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	30,749
2019	65,948
2018	36,731
2017	27,012
2016	33,423
Prior	92,217
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	446
Total	286,526
Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	72
2019	2,763
2018	2,734
2017	8,776
2016	6,430
Prior	9,955
Revolving loans amortized cost basis	205,010
Revolving loans converted to term loans	16,081
Total	251,821
Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	135
2019	0
2018	2,557
2017	10,766
2016	7,856
Prior	28,562
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	49,876	53,146
Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,079
2019	2,918
2018	1,071
2017	1,165
2016	1,936
Prior	1,988
Revolving loans amortized cost basis	71,930
Revolving loans converted to term loans	2,245
Total	85,332
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,584,365
2019	991,454
2018	900,661
2017	911,815
2016	742,482
Prior	2,196,742
Revolving loans amortized cost basis	801,695
Revolving loans converted to term loans	37,456
Total	8,166,670	7,321,402
Pass [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	58,626
2019	166,910
2018	75,223
2017	67,777
2016	43,833
Prior	79,031
Revolving loans amortized cost basis	299,536
Revolving loans converted to term loans	9,139
Total	800,075
Pass [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26,248
2019	13,448
2018	46,979
2017	76,029
2016	27,432
Prior	90,955
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	281,091
Pass [Member] \| SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,097,150
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,097,150
Pass [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	364,047
2019	722,734
2018	719,239
2017	703,597
2016	614,850
Prior	1,897,358
Revolving loans amortized cost basis	192,321
Revolving loans converted to term loans	20,802
Total	5,234,948
Pass [Member] \| Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,259
2019	16,733
2018	17,013
2017	17,780
2016	10,592
Prior	5
Revolving loans amortized cost basis	52,949
Revolving loans converted to term loans	5,484
Total	125,815
Pass [Member] \| Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	30,749
2019	65,948
2018	36,731
2017	26,637
2016	33,192
Prior	89,651
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	282,908
Pass [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	72
2019	2,763
2018	1,852
2017	8,064
2016	2,795
Prior	9,955
Revolving loans amortized cost basis	185,698
Revolving loans converted to term loans	327
Total	211,526
Pass [Member] \| Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	135
2019	0
2018	2,557
2017	10,766
2016	7,856
Prior	28,115
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	49,429
Pass [Member] \| Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,079
2019	2,918
2018	1,067
2017	1,165
2016	1,932
Prior	1,672
Revolving loans amortized cost basis	71,191
Revolving loans converted to term loans	1,704
Total	83,728
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6,650
2019	5,593
2018	14,759
2017	18,842
2016	5,724
Prior	70,767
Revolving loans amortized cost basis	22,353
Revolving loans converted to term loans	4,848
Total	149,536	173,486
Special Mention [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,013
2019	240
2018	5,074
2017	563
2016	401
Prior	4,647
Revolving loans amortized cost basis	5,531
Revolving loans converted to term loans	1,459
Total	19,928
Special Mention [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	1,144
2016	1,370
Prior	7,099
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	9,613
Special Mention [Member] \| SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [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
Special Mention [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,637
2019	5,353
2018	9,685
2017	16,423
2016	3,953
Prior	56,510
Revolving loans amortized cost basis	1,339
Revolving loans converted to term loans	0
Total	97,900
Special Mention [Member] \| Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [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
Special Mention [Member] \| Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	1,925
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,925
Special Mention [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	712
2016	0
Prior	0
Revolving loans amortized cost basis	14,750
Revolving loans converted to term loans	3,389
Total	18,851
Special Mention [Member] \| Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	447
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	447
Special Mention [Member] \| Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	139
Revolving loans amortized cost basis	733
Revolving loans converted to term loans	0
Total	872
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,898
2019	151
2018	8,282
2017	12,330
2016	7,130
Prior	23,859
Revolving loans amortized cost basis	17,659
Revolving loans converted to term loans	15,019
Total	86,328	73,431
Substandard [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,898
2019	151
2018	1,917
2017	1,987
2016	522
Prior	36
Revolving loans amortized cost basis	12,860
Revolving loans converted to term loans	1,364
Total	20,735
Substandard [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,042
2017	2,627
2016	1,411
Prior	4,372
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	9,452
Substandard [Member] \| SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [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
Substandard [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	4,437
2017	7,341
2016	1,327
Prior	18,633
Revolving loans amortized cost basis	231
Revolving loans converted to term loans	303
Total	32,272
Substandard [Member] \| Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [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
Substandard [Member] \| Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	375
2016	231
Prior	641
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	446
Total	1,693
Substandard [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	882
2017	0
2016	3,635
Prior	0
Revolving loans amortized cost basis	4,562
Revolving loans converted to term loans	12,365
Total	21,444
Substandard [Member] \| Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [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
Substandard [Member] \| Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	4
2017	0
2016	4
Prior	177
Revolving loans amortized cost basis	6
Revolving loans converted to term loans	541
Total	732
Doubtful [Member]
Financing Receivable, Credit Quality Indicator [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	$ 0
Doubtful [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [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
Doubtful [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [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
Doubtful [Member] \| SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [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
Doubtful [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [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
Doubtful [Member] \| Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0

Loans and Lease Finance Receivables and Allowance for Credit Losses - Summary of loans by type and origination year, according to our internal risk ratings (Detail) - USD ($)
$ in Thousands