FAIR VALUE MEASUREMENTS - Significant Unobservable Inputs (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value Inputs Assets Quantitative Information [Line Items]
Other investments, at fair value	$ 954,571	$ 996,751
Fixed maturities, available for sale	11,723,368	11,326,894
Significant unobservable inputs (Level 3)
Fair Value Inputs Assets Quantitative Information [Line Items]
Other investments, at fair value	94,635	141,174
Fixed maturities, available for sale	133,468	$ 119,104
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow
Fair Value Inputs Assets Quantitative Information [Line Items]
Other investments, at fair value	$ 4,684
Estimated maturity date	5 years
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Estimated maturity date	5 years
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Default rate
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.045
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Default rate | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.045
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Loss severity rate
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.500
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Loss severity rate | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.500
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Collateral spread
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.030
Significant unobservable inputs (Level 3) | Other investments - CLO-Equities | Discounted cash flow | Collateral spread | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.030
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow
Fair Value Inputs Assets Quantitative Information [Line Items]
Other investments, at fair value	$ 17,097
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Estimated maturity date	2 years
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Minimum
Fair Value Inputs Assets Quantitative Information [Line Items]
Estimated maturity date	1 year
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Estimated maturity date	2 years
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Default rate
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.005
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Default rate | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.005
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Discount rate
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.079
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Discount rate | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.079
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Loss absorption yield
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.010
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Discounted cash flow | Loss absorption yield | Weighted average
Fair Value Inputs Assets Quantitative Information [Line Items]
Unobservable input (as a percent)	0.010
Significant unobservable inputs (Level 3) | Other investments - Other privately held investments | Valuation, Market Approach
Fair Value Inputs Assets Quantitative Information [Line Items]
Other investments, at fair value	$ 73,000