Increase (Decrease) in Carrying Amount of Deferred Sales Inducements (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
DSI
Capitalization		$ 1
Accretion (amortization) expense	$ (305)	(219)
Unlocking	12	(38)
Increase (decrease) in DSI carrying amount	$ (293)	$ (256)

Amount of addition in deferred sales inducement cost.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6481800&loc=d3e11332-158416

Name:	us-gaap_DeferredSalesInducementsAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration