ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Changes in AOCI by Component (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning balance	$ 11,206,826	$ 7,042,788	$ 8,324,285
Ending balance	13,539,463	11,206,826	7,042,788
Unrealized Gains and Losses on Investments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning balance	1,415,631	(1,404,209)
Other comprehensive income (loss) before reclassifications	2,040,482	2,833,888
Other comprehensive income (loss) relating to other-than-temporary impaired investments for which a portion has been recognized in earnings	24,250	(3,574)
Amounts reclassified from accumulated other comprehensive income (loss)	63,315	(10,474)
Ending balance	3,543,678	1,415,631	(1,404,209)
Offset of net unrealized losses in AOCI due to impact of net unrealized (loss) on insurance assets and liabilities if recognized as income	(2,000,000)	(776,900)	613,400
Accumulated Gain and Loss on Derivatives
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning balance	(7,989)	(7)
Other comprehensive income (loss) before reclassifications	(2,122)	(9,781)
Other comprehensive income (loss) relating to other-than-temporary impaired investments for which a portion has been recognized in earnings	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	2,450	1,799
Ending balance	(7,661)	(7,989)	(7)
Total Accumulated Other Comprehensive Income (Loss)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning balance	1,407,642	(1,404,216)	23,816
Other comprehensive income (loss) before reclassifications	2,038,360	2,824,107
Other comprehensive income (loss) relating to other-than-temporary impaired investments for which a portion has been recognized in earnings	24,250	(3,574)
Amounts reclassified from accumulated other comprehensive income (loss)	65,765	(8,675)
Ending balance	$ 3,536,017	$ 1,407,642	$ (1,404,216)

Accumulated Other Comprehensive Income (Loss), Adjustment of Net Unrealized Losses Reported

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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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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other than temporary impairment loss (OTTI) on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss and attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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