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	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable Recorded Investment [Line Items]
2020	$ 2,470,333
2019	1,241,465
2018	690,620
2017	465,014
2016	350,781
Prior	673,255
Revolving Loans Amortized Cost Basis	720,625
Total Loans	6,612,093	$ 5,662,143
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
2020	96,868
2019	103,215
2018	42,953
2017	50,303
2016	17,876
Prior	51,411
Revolving Loans Amortized Cost Basis	161,971
Total Loans	524,597	430,705
Pegasus Bank [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	77,749
2019	71,121
2018	38,632
2017	29,364
2016	13,934
Prior	42,795
Revolving Loans Amortized Cost Basis	85,867
Total Loans	359,462
Pegasus Bank [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	19,119
2019	32,094
2018	4,321
2017	20,939
2016	3,942
Prior	7,285
Revolving Loans Amortized Cost Basis	76,104
Total Loans	163,804
Pegasus Bank [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Prior	1,331
Total Loans	1,331
Real Estate [Member] \| Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans	266,000
Real Estate [Member] \| Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
2020	51,946
2019	60,690
2018	34,475
2017	23,245
2016	20,489
Prior	43,126
Revolving Loans Amortized Cost Basis	17,439
Total Loans	251,410	246,988
Real Estate [Member] \| Farmland [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	37,586
2019	29,261
2018	21,463
2017	14,672
2016	14,438
Prior	32,080
Revolving Loans Amortized Cost Basis	7,156
Total Loans	156,656
Real Estate [Member] \| Farmland [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	12,109
2019	31,102
2018	6,920
2017	7,212
2016	5,097
Prior	9,858
Revolving Loans Amortized Cost Basis	6,620
Total Loans	78,918
Real Estate [Member] \| Farmland [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,801
2019	313
2018	1,498
2017	1,057
2016	580
Prior	810
Revolving Loans Amortized Cost Basis	1,934
Total Loans	7,993
Real Estate [Member] \| Farmland [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	450
2019	14
2018	4,594
2017	304
2016	374
Prior	378
Revolving Loans Amortized Cost Basis	1,729
Total Loans	7,843
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	155,160
2019	141,467
2018	91,755
2017	63,513
2016	53,813
Prior	127,715
Revolving Loans Amortized Cost Basis	15,549
Total Loans	648,972	621,188
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	119,516
2019	109,276
2018	77,708
2017	52,686
2016	39,161
Prior	97,123
Revolving Loans Amortized Cost Basis	11,040
Total Loans	506,510
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	35,152
2019	28,126
2018	12,584
2017	9,588
2016	12,940
Prior	27,302
Revolving Loans Amortized Cost Basis	3,957
Total Loans	129,649
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	448
2019	3,990
2018	345
2017	1,239
2016	1,324
Prior	2,823
Revolving Loans Amortized Cost Basis	85
Total Loans	10,254
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	44
2019	75
2018	1,118
2016	388
Prior	467
Revolving Loans Amortized Cost Basis	467
Total Loans	2,559
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	269,118
2019	225,385
2018	127,322
2017	92,039
2016	95,131
Prior	148,938
Revolving Loans Amortized Cost Basis	16,375
Total Loans	974,308	851,200
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	203,748
2019	170,966
2018	93,283
2017	81,087
2016	86,160
Prior	97,595
Revolving Loans Amortized Cost Basis	12,388
Total Loans	745,227
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	43,767
2019	51,241
2018	26,932
2017	10,397
2016	8,930
Prior	51,047
Revolving Loans Amortized Cost Basis	3,917
Total Loans	196,231
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,126
2019	3,087
2018	7,107
2017	555
2016	41
Prior	296
Revolving Loans Amortized Cost Basis	70
Total Loans	12,282
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	20,477
2019	91
Total Loans	20,568
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	112,236
2019	75,960
2018	17,548
2017	5,735
2016	2,165
Prior	3,044
Revolving Loans Amortized Cost Basis	12,428
Total Loans	229,116	287,138
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	98,335
2019	67,064
2018	15,893
2017	4,877
2016	1,998
Prior	2,493
Revolving Loans Amortized Cost Basis	12,078
Total Loans	202,738
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	9,837
2019	8,828
2018	1,637
2017	835
2016	167
Prior	551
Revolving Loans Amortized Cost Basis	350
Total Loans	22,205
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	4,050
2018	9
Total Loans	4,059
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	68
2018	9
2017	23
Total Loans	100
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	14
Total Loans	14
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	161,345
2019	36,971
2018	182
2017	22
2016	36
Prior	655
Revolving Loans Amortized Cost Basis	6,332
Total Loans	205,543	189,480
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	136,683
2019	30,650
2018	69
2017	22
2016	36
Prior	180
Revolving Loans Amortized Cost Basis	6,047
Total Loans	173,687
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	22,814
2019	6,202
2018	113
Prior	475
Revolving Loans Amortized Cost Basis	285
Total Loans	29,889
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,848
2019	119
Total Loans	1,967
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
2020	218,620
2019	179,723
2018	111,388
2017	82,824
2016	67,612
Prior	193,487
Total Loans	853,654	834,849
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	193,583
2019	152,017
2018	87,058
2017	68,286
2016	52,044
Prior	151,406
Total Loans	704,394
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	21,833
2019	24,877
2018	22,230
2017	12,256
2016	12,252
Prior	34,614
Total Loans	128,062
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	2,623
2019	1,986
2018	1,511
2017	1,991
2016	1,902
Prior	5,816
Total Loans	15,829
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	581
2019	843
2018	589
2017	291
2016	1,363
Prior	1,651
Total Loans	5,318
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	21,194
2019	18,623
2018	14,416
2017	9,609
2016	6,582
Prior	16,185
Revolving Loans Amortized Cost Basis	88,761
Total Loans	175,370	187,647
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	17,918
2019	15,800
2018	11,956
2017	7,509
2016	5,819
Prior	12,591
Revolving Loans Amortized Cost Basis	31,491
Total Loans	103,084
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	2,735
2019	2,010
2018	1,535
2017	1,914
2016	465
Prior	2,593
Revolving Loans Amortized Cost Basis	56,292
Total Loans	67,544
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	358
2019	486
2018	355
2017	121
2016	223
Prior	299
Revolving Loans Amortized Cost Basis	922
Total Loans	2,764
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	183
2019	257
2018	570
2017	65
2016	75
Prior	702
Revolving Loans Amortized Cost Basis	56
Total Loans	1,908
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	361,537
2019	250,320
2018	168,351
2017	94,228
2016	59,879
Prior	68,688
Revolving Loans Amortized Cost Basis	372,243
Total Loans	1,375,246	1,499,404
Commercial and Agricultural Non-Real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	246,924
2019	205,433
2018	137,219
2017	83,013
2016	51,528
Prior	42,830
Revolving Loans Amortized Cost Basis	281,100
Total Loans	1,048,047
Commercial and Agricultural Non-Real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	78,784
2019	37,525
2018	27,662
2017	7,598
2016	6,626
Prior	25,172
Revolving Loans Amortized Cost Basis	71,701
Total Loans	255,068
Commercial and Agricultural Non-Real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	10,273
2019	5,326
2018	1,605
2017	1,305
2016	363
Prior	384
Revolving Loans Amortized Cost Basis	16,684
Total Loans	35,940
Commercial and Agricultural Non-Real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	25,556
2019	2,036
2018	1,865
2017	2,312
2016	1,362
Prior	302
Revolving Loans Amortized Cost Basis	2,758
Total Loans	36,191
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	138,808
2019	119,017
2018	55,179
2017	19,405
2016	7,113
Prior	3,086
Revolving Loans Amortized Cost Basis	6,730
Total Loans	349,338	359,529
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	129,050
2019	110,557
2018	50,270
2017	17,947
2016	6,330
Prior	2,605
Revolving Loans Amortized Cost Basis	6,432
Total Loans	323,191
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	9,299
2019	7,265
2018	4,171
2017	1,092
2016	648
Prior	334
Revolving Loans Amortized Cost Basis	281
Total Loans	23,090
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	389
2019	895
2018	569
2017	272
2016	95
Prior	74
Revolving Loans Amortized Cost Basis	16
Total Loans	2,310
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	70
2019	300
2018	169
2017	94
2016	40
Prior	73
Revolving Loans Amortized Cost Basis	1
Total Loans	747
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
2020	883,501
2019	30,094
2018	27,051
2017	24,091
2016	20,085
Prior	16,920
Revolving Loans Amortized Cost Basis	22,797
Total Loans	1,024,539	$ 154,015
Other Loans [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	883,501
2019	30,094
2018	27,022
2017	21,115
2016	18,894
Prior	14,807
Revolving Loans Amortized Cost Basis	21,178
Total Loans	1,016,611
Other Loans [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2018	17
2017	2,963
2016	1,163
Prior	1,978
Revolving Loans Amortized Cost Basis	753
Total Loans	6,874
Other Loans [Member] \| Grade 3 [Member]

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