Loans and Allowance for Loan Losses - Summary of Non Accrual Loan (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Receivables [Abstract]
Total nonaccrual loans	$ 111,858	$ 27,078	$ 26,484
Interest foregone quarter to date	625	403	1,121
Amount of foregone interest applied to principal in the quarter	42	75	53
Interest foregone year to date	1,922	915	2,152
Amount of foregone interest applied to principal in the year	86	244	254
Interest foregone life to date	5,491	2,432	2,744
Amount of foregone interest applied to principal in the life	$ 2,155	$ 655	$ 471
Percentage of nonaccrual loans to gross loan portfolio	9.00%	2.00%	2.00%