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Summary of Business Segment Information (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Commercial Lines Segment
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations	$ 174	$ 120
Personal Lines
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations	206	293
American Reliable Insurance Company | Personal Lines
Segment Reporting Information [Line Items]
Ceded premiums written	$ (867)	$ 1,051
Quota share agreement percentage	100.00%	100.00%

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- Definition

Ceded Premiums Written, Net

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- Definition

Federal Excise Tax Expense Cessions From Insurance Operations To Reinsurance Operations

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- Definition

Quota Share Reinsurance Ceded, Percentage

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- Definition

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.

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- Details

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