Investments - Schedule of Changes in Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 759,409	$ 639,822
Included in realized gains / losses	1,213	0
Included in other comprehensive income	6,469	30,367
Acquisitions	0	0
Sales	0	0
Amortization	2,279	2,322
Other	(28,475)	(10,059)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 740,895	$ 662,452
Percentage of total	4.00%	4.00%
Fixed maturities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Percentage of total	100.00%		100.00%
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed maturities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Percentage of total	0.00%		0.00%
Fair Value, Inputs, Level 2 [Member] \| Fixed maturities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Percentage of total	96.00%		96.00%
Significant Unobservable Inputs (Level 3) \| Fixed maturities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Percentage of total	4.00%		4.00%
Asset- backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 13,177	$ 12,982
Included in realized gains / losses	0	0
Included in other comprehensive income	(250)	441
Acquisitions	0	0
Sales	0	0
Amortization	0	0
Other	(47)	(220)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 12,880	$ 13,203
Percentage of total	0.00%	0.00%
Collateralized debt obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 74,104	$ 73,369
Included in realized gains / losses	0	0
Included in other comprehensive income	(5,046)	6,306
Acquisitions	0	0
Sales	0	0
Amortization	2,275	2,315
Other	(2,234)	(2,912)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 69,099	$ 79,078
Percentage of total	1.00%	1.00%
Corporates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 672,128	$ 553,471
Included in realized gains / losses	1,213	0
Included in other comprehensive income	11,765	23,620
Acquisitions	0	0
Sales	0	0
Amortization	4	7
Other	(26,194)	(6,927)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 658,916	$ 570,171
Percentage of total	3.00%	3.00%

Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, amortization.

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- Definition

Other adjustments, including capitalized interest and foreign exchange.

+ References

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- Definition

Percent Of Available For Sale Securities At Fair Value By Valuation Level

+ References

No definition available.

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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

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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
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-Section 50
-Paragraph 2
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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

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-Publisher FASB
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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.

+ References

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- Definition

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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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

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.

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