Securities Sold Under Agreements to Repurchase - Schedule of Securities Sold under Agreements to Repurchase and Related Weighted-Average Interest Rates (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Securities Sold under Agreements to Repurchase [Abstract]
Securities sold under agreements to repurchase	$ 367,744,000	$ 334,540,000	$ 327,782,000
Average amount outstanding during the period	339,818,000	346,396,000
Maximum amount outstanding at any month-end during the period	$ 367,744,000	$ 367,884,000
Weighted average interest rate during period	0.34%	0.78%
Weighted average interest rate at end of period	0.21%	0.86%	0.53%