Reinsurance - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Purchase accounting adjustments	$ 2.0	$ 3.0
Minimum
Effects of Reinsurance [Line Items]
Unsecured reinsurance receivable percentage of shareholders' equity	3.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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