Loans Held for Investment and Allowance for Credit Losses on Loans - Age Analysis of Loans Held for Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 50,136	$ 49,793
Current Loans	5,939,768	5,612,350
Total Loans	5,989,904	5,662,143
Accruing Loans 90 Days or More Past Due	10,065	11,834
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,493
Current Loans	629,913
Total Loans	633,406	621,188
Accruing Loans 90 Days or More Past Due	192
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	739
Current Loans	910,943
Total Loans	911,682	851,200
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,825
Current Loans	252,379
Total Loans	254,204	287,138
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	601
Current Loans	200,294
Total Loans	200,895	189,480
Accruing Loans 90 Days or More Past Due	39
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	12,610
Current Loans	838,244
Total Loans	850,854	834,849
Accruing Loans 90 Days or More Past Due	1,685
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,204
Current Loans	182,644
Total Loans	184,848	187,647
Accruing Loans 90 Days or More Past Due	130
Real Estate [Member] \| Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		7,726
Current Loans		699,690
Total Loans		707,416
Accruing Loans 90 Days or More Past Due		3,799
Real Estate [Member] \| Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,199
Current Loans		1,134,976
Total Loans		1,137,175
Real Estate [Member] \| Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		7,893
Current Loans		332,679
Total Loans		340,572
Accruing Loans 90 Days or More Past Due		1,660
Real Estate [Member] \| Residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		8,065
Current Loans		912,767
Total Loans		920,832
Accruing Loans 90 Days or More Past Due		549
Real Estate [Member] \| Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,943
Current Loans	250,139
Total Loans	255,082	246,988
Accruing Loans 90 Days or More Past Due	1,406
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	10,077
Current Loans	1,700,291
Total Loans	1,710,368	1,499,404
Accruing Loans 90 Days or More Past Due	1,451
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,002
Current Loans	352,766
Total Loans	356,768	359,529
Accruing Loans 90 Days or More Past Due	545
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	9,372	6,291
Current Loans	147,580	147,724
Total Loans	156,952	154,015
Accruing Loans 90 Days or More Past Due	4,617	4,426
Commercial and Financial [Member] \| Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		5,499
Current Loans		1,448,894
Total Loans		1,454,393
Accruing Loans 90 Days or More Past Due		354
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		6,990
Current Loans		147,691
Total Loans		154,681
Accruing Loans 90 Days or More Past Due		555
Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		4,279
Current Loans		358,075
Total Loans		362,354
Accruing Loans 90 Days or More Past Due		491
Pegasus Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	270	851
Current Loans	474,575	429,854
Total Loans	474,845	430,705
Pegasus Bank [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	248,000
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	23,835	20,728
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	933
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	513
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,696
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	182
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	7,093
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,226
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,600
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		971
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		4,705
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		4,496
30 to 59 Days Past Due [Member] \| Real Estate [Member] \| Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,025
30 to 59 Days Past Due [Member] \| Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,173
30 to 59 Days Past Due [Member] \| Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,638
30 to 59 Days Past Due [Member] \| Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,356	1,670
30 to 59 Days Past Due [Member] \| Commercial and Financial [Member] \| Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,290
30 to 59 Days Past Due [Member] \| Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,167
30 to 59 Days Past Due [Member] \| Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,829
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,756	6,656
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	12
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	38
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	181
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,895
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	149
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		967
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		973
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,028
60 to 89 Days Past Due [Member] \| Real Estate [Member] \| Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	467
60 to 89 Days Past Due [Member] \| Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	811
60 to 89 Days Past Due [Member] \| Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	724
60 to 89 Days Past Due [Member] \| Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	479	8
60 to 89 Days Past Due [Member] \| Commercial and Financial [Member] \| Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,446
60 to 89 Days Past Due [Member] \| Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,376
60 to 89 Days Past Due [Member] \| Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		858
90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	21,545	22,409
90 Days and Greater [Member] \| Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,548
90 Days and Greater [Member] \| Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	188
90 Days and Greater [Member] \| Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	129
90 Days and Greater [Member] \| Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	238
90 Days and Greater [Member] \| Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,622
90 Days and Greater [Member] \| Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	829
90 Days and Greater [Member] \| Real Estate [Member] \| Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		5,159
90 Days and Greater [Member] \| Real Estate [Member] \| Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,228
90 Days and Greater [Member] \| Real Estate [Member] \| Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,215
90 Days and Greater [Member] \| Real Estate [Member] \| Residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,541
90 Days and Greater [Member] \| Real Estate [Member] \| Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,451
90 Days and Greater [Member] \| Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,093
90 Days and Greater [Member] \| Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	640
90 Days and Greater [Member] \| Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,537	4,613
90 Days and Greater [Member] \| Commercial and Financial [Member] \| Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,763
90 Days and Greater [Member] \| Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		3,447
90 Days and Greater [Member] \| Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		592
90 Days and Greater [Member] \| Pegasus Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 270	$ 851

Loans Held for Investment and Allowance for Credit Losses on Loans - Age Analysis of Loans Held for Investments (Detail) - USD ($)
$ in Thousands

Mar. 31, 2020

Dec. 31, 2019

Financing Receivable, Recorded Investment, Past Due [Line Items]

Total Past Due Loans

$ 50,136

$ 49,793

Current Loans

5,939,768

5,612,350

Total Loans

5,989,904