Recent Developments Including Mergers and Acquisitions - Additional Information (Detail) $ in Thousands	Dec. 31, 2019 USD ($)	Dec. 02, 2019	Aug. 15, 2019 USD ($)	Dec. 14, 2018 USD ($) ParkingSpaces	Aug. 31, 2018 USD ($) ft² Floor	Jan. 11, 2018 USD ($) Community Location	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Combination Separately Recognized Transactions [Line Items]
Goodwill	$ 148,604							$ 79,749	$ 54,042
Number of additional banking communities | Community						5
BFTower LLC [Member] | ParcFirst LLC [Member]
Business Combination Separately Recognized Transactions [Line Items]
Ownership interest acquired	50.00%
Payment to acquire ownership interest	$ 1,500
Citizens Bankshares, Inc [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition		Dec. 02, 2019
Total assets acquired							$ 56,000
Loans							26,000
Deposits							$ 42,000
Pegasus Bank [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition			Aug. 15, 2019
Total assets acquired			$ 651,100
Loans			389,900
Deposits			603,900
Contract price			123,500
Intangibles assets, net			9,900
Goodwill			$ 68,900
Cotter Ranch Tower [Member] | BFTower LLC [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition					Aug. 31, 2018
Contract price					$ 21,000
Number of square feet | ft²					507,000
Number of floors | Floor					36
Percentage of property leased					55.00%
Percentage of occupancy					35.00%
Percentage of occupancy including leased space					90.00%
Renovations completion year					2021
Renovations cost					$ 71,000
Tenant improvements					$ 12,000
Number of square feet to be occupied | ft²					165,000
Cotter Ranch Tower [Member] | BFTower LLC [Member] | SFPG, LLC [Member]
Business Combination Separately Recognized Transactions [Line Items]
Ownership interest acquired				42.60%
Space of parking garage | ParkingSpaces				1,568
Payment to acquire ownership interest				$ 9,800
First Bank & Trust Company [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition						Jan. 11, 2018
Total assets acquired						$ 290,000
Loans						247,000
Deposits						251,000
Intangibles assets, net						6,300
Goodwill						$ 19,100
First Bank of Chandler [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition						Jan. 11, 2018
Total assets acquired						$ 88,000
Loans						66,000
Deposits						79,000
Intangibles assets, net						2,200
Goodwill						$ 6,600
Number of locations acquired | Location						2