Schedule V - Supplemental Information Concerning Property and Casualty Insurance Operations (Parenthetical) (Detail)	Dec. 31, 2018	Dec. 31, 2017
Minimum [Member]
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Line Items]
Discount deducted from claim and claim adjustment expense reserves interest rates	3.50%	3.50%
Maximum [Member]
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Line Items]
Discount deducted from claim and claim adjustment expense reserves interest rates	8.00%	8.00%

Rate at which discount was computed for deduction from reserve for unpaid claim and claim adjustment expense by property-casualty insurance underwriter.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-18(Footnote 4))
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant