Loans Held for Investment and Allowance for Credit Losses on Loans - Gross Loans Held for Investment by Year of Origination and Internally Assigned Credit Grades (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable Recorded Investment [Line Items]
2020	$ 726,271
2019	1,705,016
2018	839,128
2017	597,052
2016	414,413
Prior	812,098
Revolving Loans Amortized Cost Basis	895,926
Total Loans	5,989,904	$ 5,662,143
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
2020	50,506
2019	113,451
2018	54,504
2017	57,720
2016	21,405
Prior	55,568
Revolving Loans Amortized Cost Basis	121,691
Total Loans	474,845	430,705
Pegasus Bank [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	35,067
2019	79,582
2018	43,442
2017	30,012
2016	16,926
Prior	45,404
Revolving Loans Amortized Cost Basis	80,175
Total Loans	330,608
Pegasus Bank [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	15,439
2019	33,869
2018	11,062
2017	27,708
2016	4,209
Prior	8,887
Revolving Loans Amortized Cost Basis	41,516
Total Loans	142,690
Pegasus Bank [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Prior	1,277
Total Loans	1,277
Pegasus Bank [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2016	270
Total Loans	270
Real Estate [Member] \| Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans	248,000
Real Estate [Member] \| Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
2020	20,980
2019	72,307
2018	38,346
2017	27,767
2016	24,431
Prior	50,380
Revolving Loans Amortized Cost Basis	20,871
Total Loans	255,082	246,988
Real Estate [Member] \| Farmland [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	13,825
2019	35,940
2018	24,768
2017	18,410
2016	16,773
Prior	37,822
Revolving Loans Amortized Cost Basis	7,733
Total Loans	155,271
Real Estate [Member] \| Farmland [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	6,615
2019	35,533
2018	7,464
2017	7,565
2016	6,670
Prior	10,788
Revolving Loans Amortized Cost Basis	9,347
Total Loans	83,982
Real Estate [Member] \| Farmland [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	540
2019	834
2018	5,337
2017	1,132
2016	589
Prior	1,715
Revolving Loans Amortized Cost Basis	3,540
Total Loans	13,687
Real Estate [Member] \| Farmland [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2018	777
2017	660
2016	399
Prior	55
Revolving Loans Amortized Cost Basis	251
Total Loans	2,142
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	33,789
2019	164,944
2018	107,608
2017	74,092
2016	61,864
Prior	173,415
Revolving Loans Amortized Cost Basis	17,694
Total Loans	633,406	621,188
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	25,303
2019	133,035
2018	92,854
2017	60,998
2016	48,931
Prior	133,987
Revolving Loans Amortized Cost Basis	10,456
Total Loans	505,564
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	8,430
2019	31,499
2018	13,264
2017	12,042
2016	12,038
Prior	35,219
Revolving Loans Amortized Cost Basis	3,224
Total Loans	115,716
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	56
2019	40
2018	641
2017	1,052
2016	497
Prior	2,668
Revolving Loans Amortized Cost Basis	3,547
Total Loans	8,501
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	370
2018	849
2016	398
Prior	1,541
Revolving Loans Amortized Cost Basis	467
Total Loans	3,625
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	108,189
2019	247,395
2018	159,339
2017	97,850
2016	111,625
Prior	169,110
Revolving Loans Amortized Cost Basis	18,174
Total Loans	911,682	851,200
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	95,360
2019	173,469
2018	133,346
2017	72,705
2016	98,735
Prior	110,808
Revolving Loans Amortized Cost Basis	14,231
Total Loans	698,654
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	11,131
2019	69,801
2018	18,589
2017	24,363
2016	12,846
Prior	57,175
Revolving Loans Amortized Cost Basis	3,801
Total Loans	197,706
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,698
2019	4,030
2018	7,213
2017	782
2016	44
Prior	971
Revolving Loans Amortized Cost Basis	142
Total Loans	14,880
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	95
2018	191
Prior	156
Total Loans	442
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	54,381
2019	113,199
2018	30,631
2017	37,189
2016	3,284
Prior	5,071
Revolving Loans Amortized Cost Basis	10,449
Total Loans	254,204	287,138
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	42,312
2019	101,895
2018	28,665
2017	36,294
2016	3,112
Prior	4,490
Revolving Loans Amortized Cost Basis	10,045
Total Loans	226,813
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	12,019
2019	9,018
2018	1,732
2017	869
2016	172
Prior	581
Revolving Loans Amortized Cost Basis	404
Total Loans	24,795
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	34
2019	2,211
2018	195
Total Loans	2,440
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	75
2018	39
2017	26
Total Loans	140
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	16
Total Loans	16
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	48,265
2019	144,875
2018	1,825
2017	23
2016	40
Prior	522
Revolving Loans Amortized Cost Basis	5,345
Total Loans	200,895	189,480
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	38,515
2019	120,390
2018	385
2017	23
2016	40
Prior	35
Revolving Loans Amortized Cost Basis	5,174
Total Loans	164,562
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	9,101
2019	21,755
2018	950
Prior	487
Revolving Loans Amortized Cost Basis	171
Total Loans	32,464
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	649
2019	2,597
2018	203
Total Loans	3,449
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	133
2018	287
Total Loans	420
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
2020	73,945
2019	249,223
2018	127,720
2017	96,050
2016	76,848
Prior	227,068
Total Loans	850,854	834,849
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	64,808
2019	217,000
2018	100,098
2017	79,709
2016	59,462
Prior	176,542
Total Loans	697,619
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	6,678
2019	29,159
2018	25,294
2017	14,288
2016	14,068
Prior	41,068
Total Loans	130,555
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	2,333
2019	2,468
2018	1,621
2017	1,796
2016	2,330
Prior	7,303
Total Loans	17,851
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	126
2019	596
2018	707
2017	257
2016	937
Prior	2,143
Total Loans	4,766
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2016	51
Prior	12
Total Loans	63
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
2020	7,608
2019	23,462
2018	17,396
2017	12,952
2016	8,038
Prior	20,022
Revolving Loans Amortized Cost Basis	95,370
Total Loans	184,848	187,647
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	6,151
2019	20,055
2018	14,680
2017	10,701
2016	7,350
Prior	15,475
Revolving Loans Amortized Cost Basis	36,405
Total Loans	110,817
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,282
2019	2,441
2018	1,640
2017	1,918
2016	494
Prior	3,384
Revolving Loans Amortized Cost Basis	58,583
Total Loans	69,742
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	25
2019	850
2018	1,002
2017	288
2016	194
Prior	436
Revolving Loans Amortized Cost Basis	288
Total Loans	3,083
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	53
2019	46
2018	74
2017	45
Prior	727
Revolving Loans Amortized Cost Basis	94
Total Loans	1,039
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	97
2019	70
Total Loans	167
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	273,937
2019	375,016
2018	191,001
2017	137,800
2016	71,518
Prior	84,603
Revolving Loans Amortized Cost Basis	576,493
Total Loans	1,710,368	1,499,404
Commercial and Agricultural Non-Real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	200,458
2019	306,072
2018	154,484
2017	122,613
2016	60,696
Prior	53,613
Revolving Loans Amortized Cost Basis	466,220
Total Loans	1,364,156
Commercial and Agricultural Non-Real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	38,024
2019	61,920
2018	32,778
2017	10,825
2016	6,101
Prior	29,242
Revolving Loans Amortized Cost Basis	103,820
Total Loans	282,710
Commercial and Agricultural Non-Real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	8,868
2019	5,720
2018	2,836
2017	1,833
2016	4,610
Prior	1,458
Revolving Loans Amortized Cost Basis	5,976
Total Loans	31,301
Commercial and Agricultural Non-Real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	26,587
2019	1,221
2018	903
2017	2,529
2016	111
Prior	290
Revolving Loans Amortized Cost Basis	437
Total Loans	32,078
Commercial and Agricultural Non-Real Estate [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	83
Revolving Loans Amortized Cost Basis	40
Total Loans	123
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	48,621
2019	172,130
2018	80,955
2017	29,889
2016	12,393
Prior	5,659
Revolving Loans Amortized Cost Basis	7,121
Total Loans	356,768	359,529
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	45,588
2019	160,489
2018	74,136
2017	27,553
2016	11,129
Prior	4,973
Revolving Loans Amortized Cost Basis	6,821
Total Loans	330,689
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	2,927
2019	10,459
2018	5,900
2017	1,963
2016	1,026
Prior	444
Revolving Loans Amortized Cost Basis	284
Total Loans	23,003
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	99
2019	915
2018	665
2017	303
2016	176
Prior	156
Revolving Loans Amortized Cost Basis	14
Total Loans	2,328
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	7
2019	267
2018	254
2017	70
2016	62
Prior	86
Revolving Loans Amortized Cost Basis	2
Total Loans	748
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
2020	6,050
2019	29,014
2018	29,803
2017	25,720
2016	22,967
Prior	20,680
Revolving Loans Amortized Cost Basis	22,718
Total Loans	156,952	$ 154,015
Other Loans [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	6,050
2019	29,014

Loans Held for Investment and Allowance for Credit Losses on Loans - Gross Loans Held for Investment by Year of Origination and Internally Assigned Credit Grades (Detail) - USD ($)
$ in Thousands