Subsidiary Dividend Restrictions - Additional Information (Detail) - Wright Flood $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Dividend Restrictions [Line Items]
Dividend rate as a percentage of net income	100.00%
Maximum dividend payout that may be made without prior approval	$ 4.8
Maximum
Dividend Restrictions [Line Items]
Dividend rate as a percentage of net income	10.00%

Amount of dividends that can be declared or paid without approval of regulatory agency.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant