INVESTMENTS - Realized Investment Gains (Losses), Net (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2021
Net Investment Income [Line Items]
Unrealized		$ (312,000)	$ 208,000
Realized		(1,595,000)	(518,000)
Realized investment gains (losses), net	$ 481,000	(1,907,000)	(310,000)	$ 7,489,000
Retained Business
Net Investment Income [Line Items]
Unrealized		(517,000)	162,000
Realized		(344,000)	(785,000)
Realized investment gains (losses), net		(861,000)	(623,000)
Ceded Business
Net Investment Income [Line Items]
Unrealized		205,000	46,000
Realized		(1,251,000)	267,000
Realized investment gains (losses), net		(1,046,000)	313,000
Fixed maturity securities
Net Investment Income [Line Items]
Unrealized		(285,000)	201,000
Realized		(624,000)	(57,000)
Realized investment gains (losses), net	(21,000)	(909,000)	144,000	1,302,000
Fixed maturity securities | Retained Business
Net Investment Income [Line Items]
Unrealized		(517,000)	160,000
Realized		(123,000)	(35,000)
Realized investment gains (losses), net		(640,000)	125,000
Fixed maturity securities | Ceded Business
Net Investment Income [Line Items]
Unrealized		232,000	41,000
Realized		(501,000)	(22,000)
Realized investment gains (losses), net		(269,000)	19,000
Equity securities
Net Investment Income [Line Items]
Unrealized		(27,000)	5,000
Realized		0	0
Realized investment gains (losses), net		(27,000)	5,000
Equity securities | Retained Business
Net Investment Income [Line Items]
Unrealized		0	0
Realized		0	0
Realized investment gains (losses), net		0	0
Equity securities | Ceded Business
Net Investment Income [Line Items]
Unrealized		(27,000)	5,000
Realized		0	0
Realized investment gains (losses), net		(27,000)	5,000
Secured receivable
Net Investment Income [Line Items]
Unrealized		0	2,000
Realized		(59,000)	0
Realized investment gains (losses), net		(59,000)	2,000
Secured receivable | Retained Business
Net Investment Income [Line Items]
Unrealized		0	2,000
Realized		0	0
Realized investment gains (losses), net		0	2,000
Secured receivable | Ceded Business
Net Investment Income [Line Items]
Unrealized		0	0
Realized		(59,000)	0
Realized investment gains (losses), net		(59,000)	0
Derivatives
Net Investment Income [Line Items]
Unrealized		0	0
Realized		(912,000)	(461,000)
Realized investment gains (losses), net	502,000	(912,000)	(461,000)	6,124,000
Derivatives | Retained Business
Net Investment Income [Line Items]
Unrealized		0	0
Realized		(221,000)	(750,000)
Realized investment gains (losses), net		(221,000)	(750,000)
Derivatives | Ceded Business
Net Investment Income [Line Items]
Unrealized		0	0
Realized		(691,000)	289,000
Realized investment gains (losses), net		$ (691,000)	$ 289,000
Mortgage loans
Net Investment Income [Line Items]
Realized investment gains (losses), net	0			53,000
Other invested assets
Net Investment Income [Line Items]
Realized investment gains (losses), net	$ 0			$ 10,000