Recent Developments Including Mergers and Acquisitions - Additional Information (Detail) $ in Thousands	Apr. 23, 2019 USD ($)	Dec. 14, 2018 USD ($) ParkingSpaces	Aug. 31, 2018 USD ($) ft² Floor	Jan. 11, 2018 USD ($) Community Location	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Combination Separately Recognized Transactions [Line Items]
Goodwill					$ 79,749	$ 79,749
Number of additional banking communities | Community				5
Pegasus Bank [Member]
Business Combination Separately Recognized Transactions [Line Items]
Business acquisition, date of agreement	Apr. 23, 2019
Contract price	$ 123,500
Total assets acquired						639,100
Loans						367,400
Deposits						$ 595,300
Cotter Ranch Tower [Member] | BFTower LLC [Member]
Business Combination Separately Recognized Transactions [Line Items]
Contract price			$ 21,000
Number of square feet | ft²			507,000
Number of floors | Floor			36
Date of acquisition			Aug. 31, 2018
Percentage of property leased			55.00%
Percentage of occupancy			35.00%
Percentage of occupancy including leased space			90.00%
Renovations completion year			2020
Renovations cost			$ 70,000
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