(Favorable) Unfavorable Prior Accident Year Loss Reserve Development (Parenthetical) (Detail)	Mar. 20, 2017	Mar. 19, 2017
Claims Development [Line Items]
Ogden discount rate	(0.75%)	2.50%

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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration