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	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 2,129,465
2019	954,344
2018	804,015
2017	840,334
2016	666,584
Prior	1,975,259
Revolving loans amortized cost basis	924,822
Revolving loans converted to term loans	53,985
Total loans	8,348,808	$ 7,568,319
Commercial real estate loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	988,831
2019	698,744
2018	639,959
2017	668,892
2016	570,031
Prior	1,710,506
Revolving loans amortized cost basis	198,663
Revolving loans converted to term loans	25,883
Total loans	5,501,509
Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	14,511
2019	9,350
2018	14,945
2017	2,258
2016	0
Prior	4
Revolving loans amortized cost basis	44,077
Revolving loans converted to term loans	0
Total loans	85,145
SBA [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	47,901
2019	12,821
2018	45,854
2017	69,788
2016	29,026
Prior	95,530
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	2,976
Total loans	303,896
SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	882,986
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	882,986
Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	110,819
2019	169,991
2018	68,341
2017	59,353
2016	32,529
Prior	80,995
Revolving loans amortized cost basis	281,322
Revolving loans converted to term loans	8,712
Total loans	812,062	935,127
Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,919
2019	1,765
2018	2,347
2017	6,373
2016	2,405
Prior	320
Revolving loans amortized cost basis	332,466
Revolving loans converted to term loans	13,551
Total loans	361,146	383,709
Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,478
2019	0
2018	2,556
2017	10,249
2016	3,586
Prior	20,678
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	45,547	53,146
SFR mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	65,463
2019	59,596
2018	29,142
2017	22,452
2016	27,421
Prior	66,002
Revolving loans amortized cost basis	3
Revolving loans converted to term loans	432
Total loans	270,511
Consumer and other loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,557
2019	2,077
2018	871
2017	969
2016	1,586
Prior	1,224
Revolving loans amortized cost basis	68,291
Revolving loans converted to term loans	2,431
Total loans	86,006
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,112,914
2019	944,750
2018	763,869
2017	774,130
2016	640,874
Prior	1,893,124
Revolving loans amortized cost basis	880,898
Revolving loans converted to term loans	35,633
Total loans	8,046,192	7,321,402
Pass [Member] \| Commercial real estate loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	979,499
2019	691,091
2018	607,753
2017	617,640
2016	550,105
Prior	1,646,876
Revolving loans amortized cost basis	192,583
Revolving loans converted to term loans	24,548
Total loans	5,310,095
Pass [Member] \| Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	14,511
2019	9,350
2018	14,945
2017	2,258
2016	0
Prior	4
Revolving loans amortized cost basis	44,077
Revolving loans converted to term loans	0
Total loans	85,145
Pass [Member] \| SBA [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	47,901
2019	12,821
2018	44,950
2017	58,839
2016	26,136
Prior	86,085
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	2,976
Total loans	279,708
Pass [Member] \| SBA - Paycheck Protection Program (PPP) [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	882,986
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	882,986
Pass [Member] \| Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	104,478
2019	168,050
2018	62,453
2017	56,043
2016	32,149
Prior	76,019
Revolving loans amortized cost basis	257,250
Revolving loans converted to term loans	6,058
Total loans	762,500
Pass [Member] \| Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,041
2019	1,765
2018	1,199
2017	5,680
2016	120
Prior	320
Revolving loans amortized cost basis	319,211
Revolving loans converted to term loans	363
Total loans	329,699
Pass [Member] \| Municipal Lease Finance Receivables [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,478
2019	0
2018	2,556
2017	10,249
2016	3,586
Prior	20,266
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	45,135
Pass [Member] \| SFR mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	65,463
2019	59,596
2018	29,142
2017	22,452
2016	27,192
Prior	62,593
Revolving loans amortized cost basis	3
Revolving loans converted to term loans	0
Total loans	266,441
Pass [Member] \| Consumer and other loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,557
2019	2,077
2018	871
2017	969
2016	1,586
Prior	961
Revolving loans amortized cost basis	67,774
Revolving loans converted to term loans	1,688
Total loans	84,483
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	12,205
2019	8,243
2018	32,305
2017	50,344
2016	18,829
Prior	61,325
Revolving loans amortized cost basis	36,887
Revolving loans converted to term loans	3,659
Total loans	223,797	173,486
Special Mention [Member] \| Commercial real estate loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	9,332
2019	7,162
2018	30,049
2017	43,870
2016	17,398
Prior	49,840
Revolving loans amortized cost basis	5,720
Revolving loans converted to term loans	994
Total loans	164,365
Special Mention [Member] \| Construction [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 loans	0
Special Mention [Member] \| SBA [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	5,446
2016	1,336
Prior	5,648
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	12,430
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 loans	0
Special Mention [Member] \| Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,995
2019	1,081
2018	1,892
2017	1,028
2016	95
Prior	4,882
Revolving loans amortized cost basis	17,395
Revolving loans converted to term loans	1,132
Total loans	29,500
Special Mention [Member] \| Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	878
2019	0
2018	364
2017	0
2016	0
Prior	0
Revolving loans amortized cost basis	13,255
Revolving loans converted to term loans	1,511
Total loans	16,008
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
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	412
Special Mention [Member] \| SFR mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	452
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	452
Special Mention [Member] \| Consumer and other loans [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	517
Revolving loans converted to term loans	22
Total loans	630
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,346
2019	1,351
2018	7,841
2017	15,860
2016	6,881
Prior	20,810
Revolving loans amortized cost basis	7,037
Revolving loans converted to term loans	14,693
Total loans	78,819	73,431
Substandard [Member] \| Commercial real estate loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	491
2018	2,157
2017	7,382
2016	2,528
Prior	13,790
Revolving loans amortized cost basis	360
Revolving loans converted to term loans	341
Total loans	27,049
Substandard [Member] \| Construction [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 loans	0
Substandard [Member] \| SBA [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	904
2017	5,503
2016	1,554
Prior	3,797
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	0
Total loans	11,758
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 loans	0
Substandard [Member] \| Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,346
2019	860
2018	3,996
2017	2,282
2016	285
Prior	94
Revolving loans amortized cost basis	6,677
Revolving loans converted to term loans	1,522
Total loans	20,062
Substandard [Member] \| Dairy & Livestock and Agribusiness [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	784
2017	693
2016	2,285
Prior	0
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	11,677
Total loans	15,439
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 loans	0
Substandard [Member] \| SFR mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	229
Prior	2,957
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	432
Total loans	3,618
Substandard [Member] \| Consumer and other loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	172
Revolving loans amortized cost basis	0
Revolving loans converted to term loans	721
Total loans	893
Doubtful & Loss [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 loans	0	$ 0
Doubtful & Loss [Member] \| Commercial real estate 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 loans	0
Doubtful & Loss [Member] \| Construction [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 loans	0
Doubtful & Loss [Member] \| SBA [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 loans	0
Doubtful & Loss [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 loans	0
Doubtful & Loss [Member] \| Commercial and Industrial [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