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	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable Recorded Investment [Line Items]
2020	$ 2,076,792
2019	1,417,140
2018	764,257
2017	547,712
2016	384,205
Prior	749,227
Revolving Loans Amortized Cost Basis	735,621
Total Loans	6,674,954	$ 5,662,143
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
2020	72,981
2019	108,242
2018	48,289
2017	52,447
2016	20,549
Prior	51,954
Revolving Loans Amortized Cost Basis	130,342
Total Loans	484,804	430,705
Pegasus Bank [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	55,924
2019	73,386
2018	41,076
2017	29,680
2016	15,297
Prior	42,601
Revolving Loans Amortized Cost Basis	91,378
Total Loans	349,342
Pegasus Bank [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	17,057
2019	34,856
2018	7,213
2017	22,767
2016	4,652
Prior	8,014
Revolving Loans Amortized Cost Basis	38,964
Total Loans	133,523
Pegasus Bank [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Prior	1,339
Total Loans	1,339
Pegasus Bank [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2016	600
Total Loans	600
Real Estate [Member] \| Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans	246,000
Real Estate [Member] \| Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
2020	35,792
2019	68,069
2018	35,797
2017	25,695
2016	23,121
Prior	47,899
Revolving Loans Amortized Cost Basis	19,763
Total Loans	256,136	246,988
Real Estate [Member] \| Farmland [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	27,303
2019	32,686
2018	22,385
2017	16,365
2016	15,894
Prior	35,182
Revolving Loans Amortized Cost Basis	7,696
Total Loans	157,511
Real Estate [Member] \| Farmland [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	7,741
2019	34,758
2018	7,341
2017	7,582
2016	6,262
Prior	10,985
Revolving Loans Amortized Cost Basis	8,486
Total Loans	83,155
Real Estate [Member] \| Farmland [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	748
2019	625
2018	5,313
2017	1,109
2016	584
Prior	1,353
Revolving Loans Amortized Cost Basis	3,320
Total Loans	13,052
Real Estate [Member] \| Farmland [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2018	758
2017	639
2016	381
Prior	379
Revolving Loans Amortized Cost Basis	261
Total Loans	2,418
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	109,703
2019	146,884
2018	102,327
2017	68,444
2016	58,386
Prior	149,634
Revolving Loans Amortized Cost Basis	16,038
Total Loans	651,416	621,188
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	93,204
2019	115,392
2018	88,126
2017	56,119
2016	43,573
Prior	117,406
Revolving Loans Amortized Cost Basis	9,505
Total Loans	523,325
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	16,310
2019	31,307
2018	12,723
2017	10,742
2016	13,926
Prior	29,741
Revolving Loans Amortized Cost Basis	3,324
Total Loans	118,073
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	142
2019	107
2018	599
2017	1,583
2016	495
Prior	1,380
Revolving Loans Amortized Cost Basis	2,742
Total Loans	7,048
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	47
2019	78
2018	879
2016	392
Prior	1,107
Revolving Loans Amortized Cost Basis	467
Total Loans	2,970
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	214,845
2019	250,360
2018	130,840
2017	114,570
2016	102,520
Prior	159,673
Revolving Loans Amortized Cost Basis	17,372
Total Loans	990,180	851,200
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	188,253
2019	178,055
2018	105,465
2017	90,957
2016	91,046
Prior	107,176
Revolving Loans Amortized Cost Basis	13,590
Total Loans	774,542
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	25,466
2019	68,282
2018	18,066
2017	23,070
2016	11,432
Prior	52,193
Revolving Loans Amortized Cost Basis	3,712
Total Loans	202,221
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,126
2019	3,929
2018	7,118
2017	543
2016	42
Prior	155
Revolving Loans Amortized Cost Basis	70
Total Loans	12,983
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	94
2018	191
Prior	149
Total Loans	434
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	79,269
2019	87,273
2018	30,278
2017	6,412
2016	3,046
Prior	4,649
Revolving Loans Amortized Cost Basis	14,671
Total Loans	225,598	287,138
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	66,608
2019	76,743
2018	28,386
2017	5,535
2016	2,880
Prior	4,081
Revolving Loans Amortized Cost Basis	14,229
Total Loans	198,462
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	12,612
2019	8,249
2018	1,698
2017	853
2016	166
Prior	568
Revolving Loans Amortized Cost Basis	442
Total Loans	24,588
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	184
Total Loans	2,429
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	70
2018	10
2017	24
Total Loans	104
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	15
Total Loans	15
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	114,754
2019	85,839
2018	580
2017	22
2016	37
Prior	513
Revolving Loans Amortized Cost Basis	4,759
Total Loans	206,504	189,480
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	94,678
2019	72,479
2018	69
2017	22
2016	37
Prior	32
Revolving Loans Amortized Cost Basis	4,727
Total Loans	172,044
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	18,660
2019	11,920
2018	114
Prior	481
Revolving Loans Amortized Cost Basis	32
Total Loans	31,207
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,416
2019	1,440
2018	397
Total Loans	3,253
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
2020	155,132
2019	205,849
2018	120,514
2017	90,754
2016	73,054
Prior	215,661
Total Loans	860,964	834,849
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	135,181
2019	176,422
2018	94,426
2017	76,299
2016	56,326
Prior	169,576
Total Loans	708,230
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	16,067
2019	26,417
2018	23,633
2017	12,417
2016	13,232
Prior	37,470
Total Loans	129,236
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	3,796
2019	2,195
2018	1,597
2017	1,737
2016	2,340
Prior	6,592
Total Loans	18,257
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	88
2019	815
2018	858
2017	301
2016	1,105
Prior	2,023
Total Loans	5,190
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2016	51
Total Loans	51
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
2020	15,350
2019	20,467
2018	15,839
2017	11,869
2016	7,422
Prior	17,752
Revolving Loans Amortized Cost Basis	92,140
Total Loans	180,839	187,647
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	13,054
2019	17,126
2018	13,224
2017	9,660
2016	6,747
Prior	13,647
Revolving Loans Amortized Cost Basis	32,726
Total Loans	106,184
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	2,064
2019	2,381
2018	1,545
2017	1,997
2016	415
Prior	2,999
Revolving Loans Amortized Cost Basis	59,063
Total Loans	70,464
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	180
2019	890
2018	996
2017	161
2016	226
Prior	386
Revolving Loans Amortized Cost Basis	311
Total Loans	3,150
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	52
2018	74
2017	51
2016	34
Prior	720
Revolving Loans Amortized Cost Basis	40
Total Loans	971
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	70
Total Loans	70
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	334,972
2019	268,939
2018	183,157
2017	127,834
2016	66,706
Prior	76,932
Revolving Loans Amortized Cost Basis	411,983
Total Loans	1,470,523	1,499,404
Commercial and Agricultural Non-Real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	245,805
2019	218,847
2018	148,454
2017	114,049
2016	56,916
Prior	48,438
Revolving Loans Amortized Cost Basis	310,921
Total Loans	1,143,430
Commercial and Agricultural Non-Real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	52,956
2019	46,418
2018	31,373
2017	9,951
2016	8,123
Prior	27,830
Revolving Loans Amortized Cost Basis	95,956
Total Loans	272,607
Commercial and Agricultural Non-Real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	9,530
2019	2,634
2018	2,494
2017	1,473
2016	1,517
Prior	398
Revolving Loans Amortized Cost Basis	4,724
Total Loans	22,770
Commercial and Agricultural Non-Real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	26,681
2019	989
2018	836
2017	2,361
2016	150
Prior	266
Revolving Loans Amortized Cost Basis	377
Total Loans	31,660
Commercial and Agricultural Non-Real Estate [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	51
Revolving Loans Amortized Cost Basis	5
Total Loans	56
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	103,379
2019	144,087
2018	68,325
2017	24,860
2016	9,529
Prior	4,236
Revolving Loans Amortized Cost Basis	6,324
Total Loans	360,740	359,529
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	97,332
2019	134,078
2018	62,491
2017	23,064
2016	8,531
Prior	3,601
Revolving Loans Amortized Cost Basis	6,040
Total Loans	335,137
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	5,823
2019	8,919
2018	5,049
2017	1,440
2016	822
Prior	451
Revolving Loans Amortized Cost Basis	268
Total Loans	22,772
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	207
2019	866
2018	574
2017	303
2016	127
Prior	114
Revolving Loans Amortized Cost Basis	15
Total Loans	2,206
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	17
2019	224
2018	211
2017	53
2016	49
Prior	70
Revolving Loans Amortized Cost Basis	1
Total Loans	625
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
2020	840,615
2019	31,131
2018	28,311
2017	24,805
2016	19,835
Prior	20,324
Revolving Loans Amortized Cost Basis	22,229
Total Loans	987,250	$ 154,015
Other Loans [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	840,615
2019	31,131
2018	28,254
2017	21,729
2016	18,562
Prior	17,839
Revolving Loans Amortized Cost Basis	20,228
Total Loans	978,358

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