Securities - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) security	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Debt and Equity Securities, FV-NI [Line Items]
Number of securities holdings | security	0		0
Shareholders' equity percentage	10.00%		10.00%
Tax provision related to net realized gains	$ 31	$ 0
Collateral Pledged
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, trading, restricted	$ 269,591		$ 290,717