Investment Securities - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 USD ($) Investmentsecurities	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Investment Securities [Line Items]
Investment securities sold	$ 0	$ 0
Securities Pledged As Collateral	569,296,000		$ 597,591,000
Residential real estate mortgage-backed securities	$ 1,026,710,000
Life of mortgage-backed securities	5 years 1 month 6 days
Obligations of U.S. Government Agencies [Member]
Investment Securities [Line Items]
Percentage of aggregate depreciation in unrealized losses	(1.00%)
Obligations of States and Political Subdivisions [Member]
Investment Securities [Line Items]
Available for sale securities in unrealized loss position | Investmentsecurities	13
Percentage of aggregate depreciation in unrealized losses	(2.00%)
Asset-backed Securities [Member]
Investment Securities [Line Items]
Available for sale securities in unrealized loss position | Investmentsecurities	28
Percentage of aggregate depreciation in unrealized losses	(1.30%)