Reinsurance - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Maximum amount of mortality risk retained	$ 1,000
Reinsurance receivables	200	$ 166
Reinsurance payables - net	$ 195	$ 203
GMIB
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of account values for variable annuity contracts reinsured	33.00%	34.00%
GMDB
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of account values for variable annuity contracts reinsured	4.00%	4.00%

The carrying amount as of the balance sheet date of the known and estimated amounts owed to insurers under reinsurance treaties or other arrangements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.13(a)(3),(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),6)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Stated amount that is the upper retention limit per entity policy.

+ References

No definition available.

+ Details

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

- Definition

Percentage of risk reinsured in excess of stated retention per entity policy.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
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