Net Realized Investment Gains (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses)	$ 11,774	$ 31
Fixed maturity AFS securities
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses)	11,504	77
Mortgage loans on real estate
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses)	343	58
VOBA
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses)	$ (73)	$ (104)

The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 325
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031664&loc=d3e22529-158502

Name:	us-gaap_RealizedInvestmentGainsLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration