Securities - Additional Information (Detail) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) security	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Debt and Equity Securities, FV-NI [Line Items]
Number of securities holdings | security	0	0	0
Shareholders' equity percentage	10.00%	10.00%	10.00%
Tax provision related to net realized gains	$ 0	$ 31
Collateral Pledged
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, trading, restricted	$ 261,059	$ 261,059	$ 290,717