Securities Sold Under Agreements to Repurchase - Schedule of Securities Sold under Agreements to Repurchase and Related Weighted-Average Interest Rates (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Securities Sold Under Agreements To Repurchase [Abstract]
Outstanding at end of period	$ 337,551,000	$ 319,831,000	$ 362,294,000
Average amount outstanding	344,294,000	342,797,000
Maximum amount outstanding at any month-end	$ 367,884,000	$ 364,001,000
Weighted average interest rate during period	0.80%	0.52%
Weighted average interest rate at end of period	0.74%	0.74%