Schedule of Deferred Sales Inducement Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Deferred Sales Inducements [Roll Forward]
Balance, beginning of year	$ 764,554	$ 1,110,192	$ 847,000
Capitalization	14,726	29,176	48,546
Amortization	(207,629)	(277,616)	(284,883)
Interest	23,107	28,569	33,927
Change in shadow DSI	(163,440)	(125,767)	465,602
Balance, end of year	$ 431,318	$ 764,554	$ 1,110,192

Amount of unrealized investment gain (loss) which decreases (increases) deferred sales inducement cost.

No definition available.

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- Definition

Amount of addition in deferred sales inducement cost.

+ References

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

+ Details

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- Definition

Amount of increase (decrease) in deferred sales inducement cost, classified as other.

+ References

No definition available.

+ Details

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- Definition

Amount of amortization expense (reversal of expense) for deferred sales inducement cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 2: 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

+ Details

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- Definition

Amount, after accumulated amortization, of deferred sales inducement cost.

+ References

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

+ Details

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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