Securities Sold Under Agreements to Repurchase - Schedule of Securities Sold under Agreements to Repurchase and Related Weighted-Average Interest Rates (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Securities Sold under Agreements to Repurchase [Abstract]
Securities sold under agreements to repurchase	$ 318,067,000	$ 327,782,000	$ 342,480,000
Average amount outstanding during the period	329,091,000	337,786,000	361,261,000
Maximum amount outstanding at any month-end during the period	$ 318,067,000	$ 337,185,000	$ 367,884,000
Weighted average interest rate during period	0.47%	0.55%	0.74%
Weighted average interest rate at end of period	0.22%	0.53%	0.79%