Loans and Allowance for Loan Losses - Summary of Aging of Loans (Parenthetical) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Receivables [Abstract]
Loan premiums	$ 4,358	$ 5,758
Capitalized loan origination costs	$ 21,481	$ 18,403