Securities Sold under Agreements to Repurchase - Summary of Securities Sold Under Agreements to Repurchase (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Amount outstanding at December 31	$ 266,045,000	$ 154,240,000	$ 158,990,000
Weighted average rate at December 31	0.96%	0.82%	0.32%
Maximum amount outstanding at any month end	$ 307,235,000	$ 174,150,000	$ 228,848,000
Daily average balance outstanding during the year	$ 224,361,000	$ 147,944,000	$ 189,684,000
Weighted average rate during the year	1.05%	0.66%	0.26%