Insurance Activity - Components of Liability for Losses and Loss Adjustment Reserves (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Total losses and loss adjustment reserves	$ 474	$ 811	$ 5,063
Case-basis reserves [Member]
Effects of Reinsurance [Line Items]
Total losses and loss adjustment reserves	151	553
IBNR reserves [Member]
Effects of Reinsurance [Line Items]
Total losses and loss adjustment reserves	1
Premium deficiency reserves [Member]
Effects of Reinsurance [Line Items]
Total losses and loss adjustment reserves	$ 322	$ 258