Loans - Performance of the Loan Portfolio and its Impact on the Allowance for Credit Losses (Detail) $ in Thousands	Mar. 31, 2020 USD ($)
Residential Real Estate [Member] | Non PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	$ 96,916
Term Loans Amortized Cost Basis by Origination Year 2019	331,791
Term Loans Amortized Cost Basis by Origination Year 2018	342,777
Term Loans Amortized Cost Basis by Origination Year 2017	238,128
Term Loans Amortized Cost Basis by Origination Year 2016	195,963
Term Loans Amortized Cost Basis by Origination Year Prior	664,284
Revolving loans amortized cost	667,381
Total	2,537,240
Residential Real Estate [Member] | PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	98
Term Loans Amortized Cost Basis by Origination Year 2017	3
Term Loans Amortized Cost Basis by Origination Year 2016	768
Term Loans Amortized Cost Basis by Origination Year Prior	35,608
Revolving loans amortized cost	6,302
Total	42,779
Residential Real Estate [Member] | Performing TDRs [Member] | Non PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	96,916
Term Loans Amortized Cost Basis by Origination Year 2019	331,639
Term Loans Amortized Cost Basis by Origination Year 2018	342,340
Term Loans Amortized Cost Basis by Origination Year 2017	236,663
Term Loans Amortized Cost Basis by Origination Year 2016	195,436
Term Loans Amortized Cost Basis by Origination Year Prior	657,475
Revolving loans amortized cost	664,308
Total	2,524,777
Residential Real Estate [Member] | Performing TDRs [Member] | PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	98
Term Loans Amortized Cost Basis by Origination Year 2016	471
Term Loans Amortized Cost Basis by Origination Year Prior	27,984
Revolving loans amortized cost	5,379
Total	33,932
Residential Real Estate [Member] | Non-performing TDRs [Member] | Non PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	152
Term Loans Amortized Cost Basis by Origination Year 2018	437
Term Loans Amortized Cost Basis by Origination Year 2017	1,465
Term Loans Amortized Cost Basis by Origination Year 2016	527
Term Loans Amortized Cost Basis by Origination Year Prior	6,809
Revolving loans amortized cost	3,073
Total	12,463
Residential Real Estate [Member] | Non-performing TDRs [Member] | PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2017	3
Term Loans Amortized Cost Basis by Origination Year 2016	297
Term Loans Amortized Cost Basis by Origination Year Prior	7,624
Revolving loans amortized cost	923
Total	8,847
Consumer and Other [Member] | Non PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	20,977
Term Loans Amortized Cost Basis by Origination Year 2019	65,629
Term Loans Amortized Cost Basis by Origination Year 2018	42,850
Term Loans Amortized Cost Basis by Origination Year 2017	25,188
Term Loans Amortized Cost Basis by Origination Year 2016	30,003
Term Loans Amortized Cost Basis by Origination Year Prior	24,017
Revolving loans amortized cost	26,536
Total	235,200
Consumer and Other [Member] | PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2017	1
Term Loans Amortized Cost Basis by Origination Year Prior	55
Revolving loans amortized cost	3
Total	59
Consumer and Other [Member] | Performing TDRs [Member] | Non PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	20,977
Term Loans Amortized Cost Basis by Origination Year 2019	65,599
Term Loans Amortized Cost Basis by Origination Year 2018	42,794
Term Loans Amortized Cost Basis by Origination Year 2017	25,055
Term Loans Amortized Cost Basis by Origination Year 2016	29,469
Term Loans Amortized Cost Basis by Origination Year Prior	23,750
Revolving loans amortized cost	26,523
Total	234,167
Consumer and Other [Member] | Performing TDRs [Member] | PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2017	1
Term Loans Amortized Cost Basis by Origination Year Prior	39
Revolving loans amortized cost	3
Total	43
Consumer and Other [Member] | Non-performing TDRs [Member] | Non PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	30
Term Loans Amortized Cost Basis by Origination Year 2018	56
Term Loans Amortized Cost Basis by Origination Year 2017	133
Term Loans Amortized Cost Basis by Origination Year 2016	534
Term Loans Amortized Cost Basis by Origination Year Prior	267
Revolving loans amortized cost	13
Total	1,033
Consumer and Other [Member] | Non-performing TDRs [Member] | PCD [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	16
Total	16
Non-PCD Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	519,352
Term Loans Amortized Cost Basis by Origination Year 2019	2,223,057
Term Loans Amortized Cost Basis by Origination Year 2018	2,011,580
Term Loans Amortized Cost Basis by Origination Year 2017	1,578,508
Term Loans Amortized Cost Basis by Origination Year 2016	1,297,863
Term Loans Amortized Cost Basis by Origination Year Prior	3,547,678
Revolving loans amortized cost	693,917
Total	11,871,955
Non-PCD Loans [Member] | Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	96,916
Term Loans Amortized Cost Basis by Origination Year 2019	331,791
Term Loans Amortized Cost Basis by Origination Year 2018	342,777
Term Loans Amortized Cost Basis by Origination Year 2017	238,128
Term Loans Amortized Cost Basis by Origination Year 2016	195,963
Term Loans Amortized Cost Basis by Origination Year Prior	664,284
Revolving loans amortized cost	667,381
Total	2,537,240
Non-PCD Loans [Member] | Residential Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	96,916
Term Loans Amortized Cost Basis by Origination Year 2019	331,772
Term Loans Amortized Cost Basis by Origination Year 2018	340,612
Term Loans Amortized Cost Basis by Origination Year 2017	235,228
Term Loans Amortized Cost Basis by Origination Year 2016	191,581
Term Loans Amortized Cost Basis by Origination Year Prior	626,533
Revolving loans amortized cost	659,493
Total	2,482,135
Non-PCD Loans [Member] | Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	272
Term Loans Amortized Cost Basis by Origination Year 2017	1,258
Term Loans Amortized Cost Basis by Origination Year 2016	3,182
Term Loans Amortized Cost Basis by Origination Year Prior	21,568
Revolving loans amortized cost	3,414
Total	29,694
Non-PCD Loans [Member] | Residential Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	19
Term Loans Amortized Cost Basis by Origination Year 2018	1,893
Term Loans Amortized Cost Basis by Origination Year 2017	1,642
Term Loans Amortized Cost Basis by Origination Year 2016	1,200
Term Loans Amortized Cost Basis by Origination Year Prior	16,183
Revolving loans amortized cost	4,474
Total	25,411
Non-PCD Loans [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	232,249
Term Loans Amortized Cost Basis by Origination Year 2019	1,074,838
Term Loans Amortized Cost Basis by Origination Year 2018	1,018,500
Term Loans Amortized Cost Basis by Origination Year 2017	934,248
Term Loans Amortized Cost Basis by Origination Year 2016	852,271
Term Loans Amortized Cost Basis by Origination Year Prior	2,279,869
Total	6,391,975
Non-PCD Loans [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	231,694
Term Loans Amortized Cost Basis by Origination Year 2019	1,068,021
Term Loans Amortized Cost Basis by Origination Year 2018	1,013,588
Term Loans Amortized Cost Basis by Origination Year 2017	908,262
Term Loans Amortized Cost Basis by Origination Year 2016	827,344
Term Loans Amortized Cost Basis by Origination Year Prior	2,162,917
Total	6,211,826
Non-PCD Loans [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	555
Term Loans Amortized Cost Basis by Origination Year 2019	6,378
Term Loans Amortized Cost Basis by Origination Year 2018	3,801
Term Loans Amortized Cost Basis by Origination Year 2017	16,580
Term Loans Amortized Cost Basis by Origination Year 2016	13,985
Term Loans Amortized Cost Basis by Origination Year Prior	79,175
Total	120,474
Non-PCD Loans [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	439
Term Loans Amortized Cost Basis by Origination Year 2018	1,111
Term Loans Amortized Cost Basis by Origination Year 2017	9,406
Term Loans Amortized Cost Basis by Origination Year 2016	10,942
Term Loans Amortized Cost Basis by Origination Year Prior	37,777
Total	59,675
Non-PCD Loans [Member] | Land, Development, Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	55,460
Term Loans Amortized Cost Basis by Origination Year 2019	414,961
Term Loans Amortized Cost Basis by Origination Year 2018	219,297
Term Loans Amortized Cost Basis by Origination Year 2017	85,096
Term Loans Amortized Cost Basis by Origination Year 2016	52,372
Term Loans Amortized Cost Basis by Origination Year Prior	101,828
Total	929,014
Non-PCD Loans [Member] | Land, Development, Construction [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	55,460
Term Loans Amortized Cost Basis by Origination Year 2019	414,429
Term Loans Amortized Cost Basis by Origination Year 2018	218,397
Term Loans Amortized Cost Basis by Origination Year 2017	84,358
Term Loans Amortized Cost Basis by Origination Year 2016	51,453
Term Loans Amortized Cost Basis by Origination Year Prior	93,530
Total	917,627
Non-PCD Loans [Member] | Land, Development, Construction [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	184
Term Loans Amortized Cost Basis by Origination Year 2018	626
Term Loans Amortized Cost Basis by Origination Year 2017	584
Term Loans Amortized Cost Basis by Origination Year Prior	6,042
Total	7,436
Non-PCD Loans [Member] | Land, Development, Construction [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	348
Term Loans Amortized Cost Basis by Origination Year 2018	274
Term Loans Amortized Cost Basis by Origination Year 2017	154
Term Loans Amortized Cost Basis by Origination Year 2016	919
Term Loans Amortized Cost Basis by Origination Year Prior	2,256
Total	3,951
Non-PCD Loans [Member] | Commercial and Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	113,750
Term Loans Amortized Cost Basis by Origination Year 2019	335,838
Term Loans Amortized Cost Basis by Origination Year 2018	388,156
Term Loans Amortized Cost Basis by Origination Year 2017	295,848
Term Loans Amortized Cost Basis by Origination Year 2016	167,254
Term Loans Amortized Cost Basis by Origination Year Prior	477,680
Total	1,778,526
Non-PCD Loans [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	113,652
Term Loans Amortized Cost Basis by Origination Year 2019	334,843
Term Loans Amortized Cost Basis by Origination Year 2018	382,869
Term Loans Amortized Cost Basis by Origination Year 2017	287,342
Term Loans Amortized Cost Basis by Origination Year 2016	161,970
Term Loans Amortized Cost Basis by Origination Year Prior	449,985
Total	1,730,661
Non-PCD Loans [Member] | Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	75
Term Loans Amortized Cost Basis by Origination Year 2017	3,026
Term Loans Amortized Cost Basis by Origination Year 2016	2,264
Term Loans Amortized Cost Basis by Origination Year Prior	25,662
Total	31,027
Non-PCD Loans [Member] | Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	98
Term Loans Amortized Cost Basis by Origination Year 2019	995
Term Loans Amortized Cost Basis by Origination Year 2018	5,212
Term Loans Amortized Cost Basis by Origination Year 2017	5,480
Term Loans Amortized Cost Basis by Origination Year 2016	3,020
Term Loans Amortized Cost Basis by Origination Year Prior	2,033
Total	16,838
Non-PCD Loans [Member] | Consumer and Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	20,977
Term Loans Amortized Cost Basis by Origination Year 2019	65,629
Term Loans Amortized Cost Basis by Origination Year 2018	42,850
Term Loans Amortized Cost Basis by Origination Year 2017	25,188
Term Loans Amortized Cost Basis by Origination Year 2016	30,003
Term Loans Amortized Cost Basis by Origination Year Prior	24,017
Revolving loans amortized cost	26,536
Total	235,200
Non-PCD Loans [Member] | Consumer and Other [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2020	20,977
Term Loans Amortized Cost Basis by Origination Year 2019	65,488
Term Loans Amortized Cost Basis by Origination Year 2018	42,744
Term Loans Amortized Cost Basis by Origination Year 2017	25,046
Term Loans Amortized Cost Basis by Origination Year 2016	29,300
Term Loans Amortized Cost Basis by Origination Year Prior	23,642
Revolving loans amortized cost	26,498
Total	233,695
Non-PCD Loans [Member] | Consumer and Other [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2017	5
Term Loans Amortized Cost Basis by Origination Year 2016	33
Term Loans Amortized Cost Basis by Origination Year Prior	108
Total	146
Non-PCD Loans [Member] | Consumer and Other [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	141
Term Loans Amortized Cost Basis by Origination Year 2018	106
Term Loans Amortized Cost Basis by Origination Year 2017	137
Term Loans Amortized Cost Basis by Origination Year 2016	670
Term Loans Amortized Cost Basis by Origination Year Prior	267
Revolving loans amortized cost	38
Total	1,359
PCD Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	1,905
Term Loans Amortized Cost Basis by Origination Year 2018	251
Term Loans Amortized Cost Basis by Origination Year 2017	3,928
Term Loans Amortized Cost Basis by Origination Year 2016	2,853
Term Loans Amortized Cost Basis by Origination Year Prior	135,080
Revolving loans amortized cost	6,305
Total	150,322
PCD Loans [Member] | Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	98
Term Loans Amortized Cost Basis by Origination Year 2017	3
Term Loans Amortized Cost Basis by Origination Year 2016	768
Term Loans Amortized Cost Basis by Origination Year Prior	35,608
Revolving loans amortized cost	6,302
Total	42,779
PCD Loans [Member] | Residential Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2016	268
Term Loans Amortized Cost Basis by Origination Year Prior	14,814
Revolving loans amortized cost	3,695
Total	18,777
PCD Loans [Member] | Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	3,849
Revolving loans amortized cost	224
Total	4,073
PCD Loans [Member] | Residential Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	98
Term Loans Amortized Cost Basis by Origination Year 2017	3
Term Loans Amortized Cost Basis by Origination Year 2016	500
Term Loans Amortized Cost Basis by Origination Year Prior	16,945
Revolving loans amortized cost	2,383
Total	19,929
PCD Loans [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	1,807
Term Loans Amortized Cost Basis by Origination Year 2017	2,801
Term Loans Amortized Cost Basis by Origination Year 2016	678
Term Loans Amortized Cost Basis by Origination Year Prior	86,995
Total	92,281
PCD Loans [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	25,820
Total	25,820
PCD Loans [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	10,792
Total	10,792
PCD Loans [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2019	1,807
Term Loans Amortized Cost Basis by Origination Year 2017	2,801
Term Loans Amortized Cost Basis by Origination Year 2016	678
Term Loans Amortized Cost Basis by Origination Year Prior	50,383
Total	55,669
PCD Loans [Member] | Land, Development, Construction [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	188
Term Loans Amortized Cost Basis by Origination Year 2016	121
Term Loans Amortized Cost Basis by Origination Year Prior	5,138
Total	5,447
PCD Loans [Member] | Land, Development, Construction [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	1,810
Total	1,810
PCD Loans [Member] | Land, Development, Construction [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	630
Total	630
PCD Loans [Member] | Land, Development, Construction [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	188
Term Loans Amortized Cost Basis by Origination Year 2016	121
Term Loans Amortized Cost Basis by Origination Year Prior	2,698
Total	3,007
PCD Loans [Member] | Commercial and Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	63
Term Loans Amortized Cost Basis by Origination Year 2017	1,123
Term Loans Amortized Cost Basis by Origination Year 2016	1,286
Term Loans Amortized Cost Basis by Origination Year Prior	7,284
Total	9,756
PCD Loans [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	15
Term Loans Amortized Cost Basis by Origination Year Prior	1,398
Total	1,413
PCD Loans [Member] | Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	405
Total	405
PCD Loans [Member] | Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2018	48
Term Loans Amortized Cost Basis by Origination Year 2017	1,123
Term Loans Amortized Cost Basis by Origination Year 2016	1,286
Term Loans Amortized Cost Basis by Origination Year Prior	5,481
Total	7,938
PCD Loans [Member] | Consumer and Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2017	1
Term Loans Amortized Cost Basis by Origination Year Prior	55
Revolving loans amortized cost	3
Total	59
PCD Loans [Member] | Consumer and Other [Member] | Pass [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year Prior	30
Revolving loans amortized cost	3
Total	33
PCD Loans [Member] | Consumer and Other [Member] | Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Term Loans Amortized Cost Basis by Origination Year 2017	1
Term Loans Amortized Cost Basis by Origination Year Prior	25
Total	$ 26