INVESTMENTS - Realized Gains (Losses) on Investments (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
Debt Securities, Available-for-Sale [Line Items]
Proceeds from maturities/prepayments	$ 422,000	$ 0	$ 0	$ 9,400,000
Fixed Maturities
Debt Securities, Available-for-Sale [Line Items]
Proceeds from sales	294,000			8,319,000
Proceeds from maturities/prepayments	108,000			828,000
Gross investment gains on sales and maturities	0			1,413,000
Gross investment losses on sales and maturities	(21,000)			(88,000)
Write-downs recognized in earnings	0			(23,000)
Noncash related proceeds	$ 20,300			$ 253,400