Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 7,014	$ 4,919
Trading Securities, Realized Gain (Loss)	612	5,024
Investment expense	(1,967)	(2,228)	$ (5,167)	$ (6,269)
Securities available-for-sale and short-term	49,985	80,999	222,278	235,092
Total net investment income	58,332	87,177	235,234	253,896
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			9,067	15,130
Trading Securities, Realized Gain (Loss)			(2,067)	8,140
Fixed Income Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	49,372	81,054	219,222	236,876
Short-Term [Member]
Investment [Line Items]
Gross Investment Income, Operating	2,395	1,986	7,671	4,124
Loans Receivable [Member]
Investment [Line Items]
Gross Investment Income, Operating	185	187	552	361
Other Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ 8,347	$ 6,178	$ 12,956	$ 18,804

Line items represent reporting 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895926&loc=d3e24721-111560

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Amount of expenses related to the generation of investment income.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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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(2))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Paragraph 1
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The sum of the realized and unrealized net gain (loss) on trading securities during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27476-111563

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