Allowance for Loan Losses - Analysis of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended							12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Allowance for loan losses, beginning of year				$ 28,543			$ 26,255	$ 28,543	$ 26,255	$ 24,406
Loans charged-off								(454)	(833)	(390)
Recoveries on loans previously charged-off								246	1,771	449
Net recoveries (charge-offs)								(208)	938	59
Provision charged to expense	$ 550	$ 75	$ 250	$ 375	$ 450	$ 450	$ 450	1,250	1,350	1,790
Allowance for loan losses, end of year	$ 29,585				$ 28,543			$ 29,585	$ 28,543	$ 26,255