Securities Sold Under Agreements to Repurchase - Schedule of Securities Sold under Agreements to Repurchase and Related Weighted-Average Interest Rates (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Securities Sold Under Agreements To Repurchase [Abstract]
Outstanding at year-end	$ 327,782,000	$ 362,294,000
Average amount outstanding	342,654,000	344,964,000
Maximum amount outstanding at any month-end	$ 367,884,000	$ 364,001,000
Weighted average interest rate during period	0.73%	0.57%
Weighted average interest rate at end of period	0.53%	0.75%