Premises and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amount charged to operating expenses for depreciation	$ 7,600	$ 7,100	$ 6,700
Amount charged to operating expenses for software amortization	2,755	4,652	6,532
Software Costs
Net Software cost included in other asset	4,000	4,000
Premises And Equipment
Rental expenses for premises and equipment	12,100	11,200	11,100
Software Amortization
Amount charged to operating expenses for software amortization	$ 1,700	$ 1,900	$ 1,700