Loans Held for Investment and Allowance for Credit Losses on Loans - Age Analysis of Loans Held for Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 58,900	$ 49,793
Current Loans	6,616,054	5,612,350
Total Loans	6,674,954	5,662,143
Accruing Loans 90 Days or More Past Due	5,382	11,834
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,507
Current Loans	648,909
Total Loans	651,416	621,188
Accruing Loans 90 Days or More Past Due	77
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	350
Current Loans	989,830
Total Loans	990,180	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	952
Current Loans	224,646
Total Loans	225,598	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	396
Current Loans	206,108
Total Loans	206,504	189,480
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	9,478
Current Loans	851,486
Total Loans	860,964	834,849
Accruing Loans 90 Days or More Past Due	1,945
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,386
Current Loans	179,453
Total Loans	180,839	187,647
Accruing Loans 90 Days or More Past Due	63
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	5,794
Current Loans	250,342
Total Loans	256,136	246,988
Accruing Loans 90 Days or More Past Due	763
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	28,663
Current Loans	1,441,860
Total Loans	1,470,523	1,499,404
Accruing Loans 90 Days or More Past Due	2,154
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,772
Current Loans	357,968
Total Loans	360,740	359,529
Accruing Loans 90 Days or More Past Due	313
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	6,002	6,291
Current Loans	981,248	147,724
Total Loans	987,250	154,015
Accruing Loans 90 Days or More Past Due	67	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
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
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
Pegasus Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	600	851
Current Loans	484,204	429,854
Total Loans	484,804	430,705
Pegasus Bank [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	246,000
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	28,485	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	415
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	50
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	952
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	396
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	3,587
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	449
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	1,649
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	19,056
30 to 59 Days Past Due [Member] \| Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,712
30 to 59 Days Past Due [Member] \| Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	219	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] \| Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,829
30 to 59 Days Past Due [Member] \| Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,167
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	8,065	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	55
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	112
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	1,316
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	171
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	888
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	4,766
60 to 89 Days Past Due [Member] \| Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	595
60 to 89 Days Past Due [Member] \| Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	162	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] \| Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		858
60 to 89 Days Past Due [Member] \| Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		1,376
90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	22,350	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	2,037
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] \| Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,575
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	766
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	3,257
90 Days and Greater [Member] \| Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,841
90 Days and Greater [Member] \| Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	465
90 Days and Greater [Member] \| Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,621	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] \| Consumer Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		592
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] \| Pegasus Bank [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 600	$ 851

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

Jun. 30, 2020

Dec. 31, 2019

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

Total Past Due Loans

$ 58,900

$ 49,793

Current Loans

6,616,054

5,612,350

Total Loans

6,674,954