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Recent Developments, Including Mergers and Acquisitions - Additional Information (Detail) $ in Thousands	Jun. 17, 2021 USD ($)	May 20, 2021 USD ($) Location	Jan. 22, 2021 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Business Combination Separately Recognized Transactions [Line Items]
Total assets				$ 11,015,287	$ 9,212,357
Loans held for investment (net of unearned interest)				6,191,230	6,394,506
Deposits				$ 9,728,389	$ 8,064,704
First National Bank and Trust [Member]
Business Combination Separately Recognized Transactions [Line Items]
Total assets		$ 284,000
Loans held for investment (net of unearned interest)		195,000
Deposits		256,000
Purchase price		21,000
Bargain purchase gain		6,000
Purchase expenses		4,000
Intangibles assets, net		$ 1,900
Subordinated Notes due 2036 [Member] | Private Placement [Member]
Business Combination Separately Recognized Transactions [Line Items]
Aggregate principal amount	$ 60,000
Fixed-to-floating rate	3.50%
Debt instrument maturity year	2036
Oklahoma [Member]
Business Combination Separately Recognized Transactions [Line Items]
Sale of Loans			$ 21,000
Deposits sold			38,000
Oklahoma [Member] | Noninterest Income [Member]
Business Combination Separately Recognized Transactions [Line Items]
Gain on transaction			$ 2,500
Oklahoma [Member] | First National Bank and Trust [Member]
Business Combination Separately Recognized Transactions [Line Items]
Number of banking locations | Location		2

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