INVESTMENT OPERATIONS - Schedule of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Net Investment Income [Line Items]
Fair Value	$ 3,025,790	$ 2,547,210
Fixed Maturities
Net Investment Income [Line Items]
Amortized Cost	2,823,881	2,633,474
Gross Unrecognized Holding Gains	201,909	0
Gross Unrecognized Holding Losses	0	(86,264)
Fair Value	3,025,790	2,547,210
Total OTTI Recognized in OCI	0	0
Red Mountain \| Fixed Maturities
Net Investment Income [Line Items]
Amortized Cost	795,881	750,474
Gross Unrecognized Holding Gains	81,022	0
Gross Unrecognized Holding Losses	0	(81,657)
Fair Value	876,903	668,817
Total OTTI Recognized in OCI	0	0
Steel City \| Fixed Maturities
Net Investment Income [Line Items]
Amortized Cost	2,028,000	1,883,000
Gross Unrecognized Holding Gains	120,887	0
Gross Unrecognized Holding Losses	0	(4,607)
Fair Value	2,148,887	1,878,393
Total OTTI Recognized in OCI	$ 0	$ 0

Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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Amount, before tax, of other-than-temporary impairment (OTTI) on investment in debt security measured at amortized cost (held-to-maturity), recognized in earnings and other comprehensive income (OCI).

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-Topic 320
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