Reinsurance - Additional Information (Detail) - state	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Transportation Network Company [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Number of States in which Entity Operates	4	1	1

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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