Fair Value of Financial Instruments - Financial Instruments Measured at Fair Value on Recurring Basis Using (Level 3) Inputs (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Embedded Derivative
Fair Value, Liabilities Measured on Recurring Basis [Roll Forward]
Beginning balance	$ 731,552	$ 596,075
Net loss for derivatives included in net investment income	0	0
Net change included in interest credited	(89,581)	58,156
Net fair value change included in other comprehensive income	0	0
Purchases, sales and settlements or maturities
Purchases	0	0
Sales	0	0
Settlements or maturities	0	0
Premiums less benefits	(11,019)	14,254
Ending balance	630,952	668,485
Investment Securities
Fair Value, Assets Measured on Recurring Basis [Roll Forward]
Beginning balance	45,307	4,346
Net loss for derivatives included in net investment income	0	0
Net change included in interest credited	0	0
Net fair value change included in other comprehensive income	0	0
Purchases, sales and settlements or maturities
Purchases	22,702	0
Sales	(14,156)	0
Settlements or maturities	0	0
Premiums less benefits	0	0
Ending balance	53,853	4,346
Equity-Indexed Options
Fair Value, Assets Measured on Recurring Basis [Roll Forward]
Beginning balance	256,005	148,006
Net loss for derivatives included in net investment income	(108,095)	66,485
Net change included in interest credited	0	0
Net fair value change included in other comprehensive income	0	0
Purchases, sales and settlements or maturities
Purchases	14,164	17,356
Sales	0	0
Settlements or maturities	(36,086)	(15,691)
Premiums less benefits	0	0
Ending balance	125,988	216,156
Separately Managed Accounts
Fair Value, Assets Measured on Recurring Basis [Roll Forward]
Beginning balance	50,503	0
Net loss for derivatives included in net investment income	0	16,532
Net change included in interest credited	0	0
Net fair value change included in other comprehensive income	80	9
Purchases, sales and settlements or maturities
Purchases	0	4,505
Sales	0	0
Settlements or maturities	0	0
Premiums less benefits	0	0
Ending balance	$ 50,583	$ 21,046

Fair value measurement with unobservable inputs reconciliation asset premiums less benefits.

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Fair value measurement with unobservable inputs reconciliation liability premiums less benefits losses.

+ References

No definition available.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis assets net change included in interest credited.

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No definition available.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis liabilities net change included in interest credited.

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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.

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

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 2
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- References

No definition available.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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Amount of gain (loss) recognized in other comprehensive income (OCI) from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sales of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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