Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of loans by type and origination year, according to our internal risk ratings (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 229,027
2019	996,807
2018	954,745
2017	997,179
2016	779,281
Prior	2,435,073
Revolving loans amortized cost basis	1,016,807
Revolving loans converted to term loans	57,233
Total	7,466,152	$ 7,568,319
Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	36,167
2019	160,951
2018	88,009
2017	76,840
2016	49,874
Prior	89,364
Revolving loans amortized cost basis	447,040
Revolving loans converted to term loans	12,516
Total	960,761
Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26,599
2019	18,009
2018	49,840
2017	82,231
2016	30,803
Prior	105,589
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	313,071
Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	153,366
2019	731,611
2018	758,170
2017	754,616
2016	635,087
Prior	2,093,573
Revolving loans amortized cost basis	201,042
Revolving loans converted to term loans	20,460
Total	5,347,925
Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	550
2019	13,414
2018	13,300
2017	35,130
2016	10,592
Prior	5
Revolving loans amortized cost basis	49,591
Revolving loans converted to term loans	5,463
Total	128,045
Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10,473
2019	66,680
2018	38,192
2017	27,198
2016	35,992
Prior	99,762
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	446
Total	278,743
Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	78
2019	2,945
2018	2,988
2017	8,831
2016	6,847
Prior	14,655
Revolving loans amortized cost basis	219,424
Revolving loans converted to term loans	16,346
Total	272,114
Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	147
2019	0
2018	3,081
2017	10,961
2016	7,912
Prior	29,186
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	51,287	53,146
Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,647
2019	3,197
2018	1,165
2017	1,372
2016	2,174
Prior	2,939
Revolving loans amortized cost basis	99,710
Revolving loans converted to term loans	2,002
Total	114,206
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	227,961
2019	991,064
2018	929,806
2017	966,220
2016	762,602
Prior	2,344,233
Revolving loans amortized cost basis	961,714
Revolving loans converted to term loans	34,641
Total	7,218,241	7,321,402
Pass [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	35,101
2019	160,551
2018	79,808
2017	74,291
2016	48,698
Prior	85,803
Revolving loans amortized cost basis	423,186
Revolving loans converted to term loans	8,849
Total	916,287
Pass [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26,599
2019	18,009
2018	48,416
2017	77,219
2016	27,922
Prior	93,865
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	292,030
Pass [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	153,366
2019	726,268
2018	743,909
2017	732,319
2016	626,561
Prior	2,021,759
Revolving loans amortized cost basis	197,335
Revolving loans converted to term loans	18,747
Total	5,220,264
Pass [Member] \| Construction Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	550
2019	13,414
2018	13,300
2017	35,130
2016	10,592
Prior	5
Revolving loans amortized cost basis	49,591
Revolving loans converted to term loans	5,463
Total	128,045
Pass [Member] \| Consumer Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10,473
2019	66,680
2018	38,192
2017	26,819
2016	35,992
Prior	96,795
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	274,951
Pass [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	78
2019	2,945
2018	1,940
2017	8,109
2016	2,831
Prior	14,655
Revolving loans amortized cost basis	192,649
Revolving loans converted to term loans	0
Total	223,207
Pass [Member] \| Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	147
2019	0
2018	3,081
2017	10,961
2016	7,912
Prior	28,739
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	50,840
Pass [Member] \| Consumer Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,647
2019	3,197
2018	1,160
2017	1,372
2016	2,094
Prior	2,612
Revolving loans amortized cost basis	98,953
Revolving loans converted to term loans	1,582
Total	112,617
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,066
2019	5,600
2018	16,677
2017	20,077
2016	9,107
Prior	66,865
Revolving loans amortized cost basis	38,814
Revolving loans converted to term loans	6,128
Total	164,334	173,486
Special Mention [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,066
2019	257
2018	7,405
2017	1,694
2016	539
Prior	3,524
Revolving loans amortized cost basis	12,598
Revolving loans converted to term loans	2,442
Total	29,525
Special Mention [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	1,177
2016	1,277
Prior	7,809
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	10,263
Special Mention [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,343
2018	9,106
2017	16,484
2016	7,211
Prior	52,995
Revolving loans amortized cost basis	3,457
Revolving loans converted to term loans	0
Total	94,596
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	1,942
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	1,942
Special Mention [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	166
2017	722
2016	0
Prior	0
Revolving loans amortized cost basis	22,150
Revolving loans converted to term loans	3,686
Total	26,724
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	80
Prior	148
Revolving loans amortized cost basis	609
Revolving loans converted to term loans	0
Total	837
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	143
2018	8,262
2017	10,882
2016	7,572
Prior	23,975
Revolving loans amortized cost basis	16,279
Revolving loans converted to term loans	16,464
Total	83,577	73,431
Substandard [Member] \| Commercial And Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	143
2018	796
2017	855
2016	637
Prior	37
Revolving loans amortized cost basis	11,256
Revolving loans converted to term loans	1,225
Total	14,949
Substandard [Member] \| Commercial Trade Financing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,424
2017	3,835
2016	1,604
Prior	3,915
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	10,778
Substandard [Member] \| Real Estate Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	5,155
2017	5,813
2016	1,315
Prior	18,819
Revolving loans amortized cost basis	250
Revolving loans converted to term loans	1,713
Total	33,065
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	379
2016	0
Prior	1,025
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	446
Total	1,850
Substandard [Member] \| Dairy And Livestock And Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	882
2017	0
2016	4,016
Prior	0
Revolving loans amortized cost basis	4,625
Revolving loans converted to term loans	12,660
Total	22,183
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	5
2017	0
2016	0
Prior	179
Revolving loans amortized cost basis	148
Revolving loans converted to term loans	420
Total	752
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] \| 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
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total	0
Doubtful [Member] \| Consumer Mortgage [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] \| Dairy And Livestock And Agribusiness [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] \| 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
Doubtful [Member] \| Consumer Other [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

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