Reinsurance - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Effects of Reinsurance [Line Items]
Reinsurance unsecured amounts due from reinsurers	$ 243,019	$ 360,254
Stockholders' Equity, Total [Member] \| Amounts Due From Reinsurers [Member]
Effects of Reinsurance [Line Items]
Unsecured amounts due from reinsurers exceeding a fixed percentage of stockholders equity	3.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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