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	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,915,829
2019	974,518
2018	881,124
2017	911,758
2016	724,436
Prior	2,120,664
Revolving loans amortized cost basis	822,289
Revolving loans converted to term loans	57,254
Total	8,407,872	$ 7,568,319
Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	86,025
2019	172,084
2018	76,932
2017	65,547
2016	42,549
Prior	85,692
Revolving loans amortized cost basis	277,849
Revolving loans converted to term loans	10,378
Total	817,056
Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	37,389
2019	13,394
2018	47,148
2017	75,776
2016	29,585
Prior	98,822
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	2,873
Total	304,987
SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,101,142
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,101,142
Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	621,687
2019	713,566
2018	702,980
2017	711,783
2016	604,699
Prior	1,840,177
Revolving loans amortized cost basis	206,705
Revolving loans converted to term loans	26,626
Total	5,428,223
Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	11,160
2019	8,614
2018	14,399
2017	15,667
2016	10,592
Prior	4
Revolving loans amortized cost basis	41,467
Revolving loans converted to term loans	0
Total	101,903
Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	52,065
2019	62,325
2018	33,614
2017	25,069
2016	28,573
Prior	72,645
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	440
Total	274,731
Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	755
2019	2,201
2018	2,524
2017	6,412
2016	3,137
Prior	341
Revolving loans amortized cost basis	223,030
Revolving loans converted to term loans	14,402
Total	252,802
Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	123
2019	0
2018	2,556
2017	10,436
2016	3,587
Prior	21,338
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	38,040	53,146
Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,483
2019	2,334
2018	971
2017	1,068
2016	1,714
Prior	1,645
Revolving loans amortized cost basis	73,238
Revolving loans converted to term loans	2,535
Total	88,988
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,906,637
2019	961,016
2018	852,750
2017	878,051
2016	702,489
Prior	2,037,779
Revolving loans amortized cost basis	781,006
Revolving loans converted to term loans	39,843
Total	8,159,571	7,321,402
Pass [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	81,480
2019	170,738
2018	72,345
2017	62,918
2016	41,860
Prior	80,669
Revolving loans amortized cost basis	255,407
Revolving loans converted to term loans	8,153
Total	773,570
Pass [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	37,389
2019	13,394
2018	46,193
2017	72,665
2016	26,687
Prior	88,255
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	2,873
Total	287,456
Pass [Member] \| SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,101,142
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,101,142
Pass [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	617,068
2019	701,648
2018	680,997
2017	684,519
2016	589,553
Prior	1,776,989
Revolving loans amortized cost basis	201,021
Revolving loans converted to term loans	26,329
Total	5,278,124
Pass [Member] \| Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	11,160
2019	8,614
2018	14,399
2017	15,667
2016	10,592
Prior	4
Revolving loans amortized cost basis	41,467
Revolving loans converted to term loans	0
Total	101,903
Pass [Member] \| Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	52,050
2019	62,087
2018	33,614
2017	25,069
2016	28,344
Prior	69,215
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	270,379
Pass [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	742
2019	2,201
2018	1,675
2017	5,709
2016	152
Prior	341
Revolving loans amortized cost basis	210,610
Revolving loans converted to term loans	494
Total	221,924
Pass [Member] \| Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	123
2019	0
2018	2,556
2017	10,436
2016	3,587
Prior	20,926
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	37,628
Pass [Member] \| Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,483
2019	2,334
2018	971
2017	1,068
2016	1,714
Prior	1,380
Revolving loans amortized cost basis	72,501
Revolving loans converted to term loans	1,994
Total	87,445
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,647
2019	12,360
2018	21,255
2017	23,694
2016	15,458
Prior	61,475
Revolving loans amortized cost basis	33,750
Revolving loans converted to term loans	2,950
Total	175,589	173,486
Special Mention [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,235
2018	3,087
2017	814
2016	241
Prior	5,015
Revolving loans amortized cost basis	15,970
Revolving loans converted to term loans	1,022
Total	27,384
Special Mention [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	1,113
2016	1,352
Prior	6,910
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	9,375
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	4,619
2019	11,125
2018	18,168
2017	21,767
2016	13,865
Prior	48,591
Revolving loans amortized cost basis	5,447
Revolving loans converted to term loans	297
Total	123,879
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	15
2019	0
2018	0
2017	0
2016	0
Prior	456
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	471
Special Mention [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	13
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	11,596
Revolving loans converted to term loans	1,631
Total	13,240
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	412
Total	412
Special Mention [Member] \| Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	91
Revolving loans amortized cost basis	737
Revolving loans converted to term loans	0
Total	828
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,545
2019	1,142
2018	7,119
2017	10,013
2016	6,489
Prior	21,410
Revolving loans amortized cost basis	7,533
Revolving loans converted to term loans	14,461
Total	72,712	73,431
Substandard [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,545
2019	111
2018	1,500
2017	1,815
2016	448
Prior	8
Revolving loans amortized cost basis	6,472
Revolving loans converted to term loans	1,203
Total	16,102
Substandard [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	955
2017	1,998
2016	1,546
Prior	3,657
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	8,156
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	793
2018	3,815
2017	5,497
2016	1,281
Prior	14,597
Revolving loans amortized cost basis	237
Revolving loans converted to term loans	0
Total	26,220
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	238
2018	0
2017	0
2016	229
Prior	2,974
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	440
Total	3,881
Substandard [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	849
2017	703
2016	2,985
Prior	0
Revolving loans amortized cost basis	824
Revolving loans converted to term loans	12,277
Total	17,638
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	0
2017	0
2016	0
Prior	174
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	541
Total	715
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
2016	0
Prior	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