Loans and Allowance for Loan Losses - Summary of Outstanding and Carrying Amounts of PCI Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Financing receivable, purchased with credit deterioration, amount at purchase price	$ 74,390	$ 86,431
Outstanding balance
Financing Receivable, Impaired [Line Items]
Financing receivable, purchased with credit deterioration, amount at purchase price	8,662		$ 9,982
Carrying amount
Financing Receivable, Impaired [Line Items]
Financing receivable, purchased with credit deterioration, amount at purchase price	$ 7,617		$ 9,297