FAIR VALUE MEASUREMENTS (Changes in Level 3 for Financial Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	$ 64,098	$ 95,770	$ 59,283	$ 152,468
Transfers into Level 3	10,060	5,285	19,245	5,285
Transfers out of Level 3	0	(489)	0	(33,222)
Included in net income	375	708	(2,791)	15,358
Included in OCI	328	(109)	446	1,162
Purchases	1,276	15,000	1,758	27,250
Sales	0	(14,749)	0	(53,754)
Settlements/ distributions	(2,291)	(1,426)	(4,095)	(14,557)
Closing balance	73,846	99,990	73,846	99,990
Change in unrealized investment gains/(losses)	144	1,194	(3,022)	3,876
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	9,818	10,262	9,672	10,299
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Included in net income	(370)	(126)	9,747	(163)
Included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements/ distributions	0	0	(9,971)	0
Closing balance	9,448	10,136	9,448	10,136
Change in unrealized investment gains/(losses)	(370)	(126)	(224)	(163)
Other liabilities | Derivative instruments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	9,818	10,262	9,672	10,299
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Included in net income	(370)	(126)	9,747	(163)
Included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements/ distributions	0	0	(9,971)	0
Closing balance	9,448	10,136	9,448	10,136
Change in unrealized investment gains/(losses)	(370)	(126)	(224)	(163)
Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	16,735	49,520	8,021	86,679
Transfers into Level 3	10,060	5,285	19,245	5,285
Transfers out of Level 3	0	(489)	0	(33,222)
Included in net income	0	0	0	(1,459)
Included in OCI	328	(109)	446	1,162
Purchases	0	0	0	9,750
Sales	0	0	0	(5,578)
Settlements/ distributions	(1,959)	(390)	(2,548)	(8,800)
Closing balance	25,164	53,817	25,164	53,817
Change in unrealized investment gains/(losses)	0	0	0	0
Fixed maturities | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	2,298	39,137	2,297	49,012
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(489)	0	(489)
Included in net income	0	0	0	(1,459)
Included in OCI	101	(97)	102	836
Purchases	0	0	0	0
Sales	0	0	0	(5,578)
Settlements/ distributions	0	0	0	(3,771)
Closing balance	2,399	38,551	2,399	38,551
Change in unrealized investment gains/(losses)	0	0	0	0
Fixed maturities | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	4,434	9,892	5,235	19,134
Transfers into Level 3	0	5,285	0	5,285
Transfers out of Level 3	0	0	0	(4,767)
Included in net income	0	0	0	0
Included in OCI	148	(13)	(64)	151
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements/ distributions	(1,959)	(390)	(2,548)	(5,029)
Closing balance	2,623	14,774	2,623	14,774
Change in unrealized investment gains/(losses)	0	0	0	0
Fixed maturities | Non-agency RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	9,562	0	0	0
Transfers into Level 3	0	0	9,185	0
Transfers out of Level 3	0	0	0	0
Included in net income	0	0	0	0
Included in OCI	70	0	447	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements/ distributions	0	0	0	0
Closing balance	9,632	0	9,632	0
Change in unrealized investment gains/(losses)	0	0	0	0
Fixed maturities | ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	441	491	489	18,533
Transfers into Level 3	10,060	0	10,060	0
Transfers out of Level 3	0	0	0	(27,966)
Included in net income	0	0	0	0
Included in OCI	9	1	(39)	175
Purchases	0	0	0	9,750
Sales	0	0	0	0
Settlements/ distributions	0	0	0	0
Closing balance	10,510	492	10,510	492
Change in unrealized investment gains/(losses)	0	0	0	0
Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	47,363	46,250	51,262	65,789
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Included in net income	375	708	(2,791)	16,817
Included in OCI	0	0	0	0
Purchases	1,276	15,000	1,758	17,500
Sales	0	(14,749)	0	(48,176)
Settlements/ distributions	(332)	(1,036)	(1,547)	(5,757)
Closing balance	48,682	46,173	48,682	46,173
Change in unrealized investment gains/(losses)	144	1,194	(3,022)	3,876
Other investments | CLO-Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	9,943	17,798	14,328	21,271
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Included in net income	(422)	(1,308)	(3,592)	(60)
Included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements/ distributions	(332)	(1,036)	(1,547)	(5,757)
Closing balance	9,189	15,454	9,189	15,454
Change in unrealized investment gains/(losses)	(422)	(1,308)	(3,592)	(60)
Other investments | Other privately held investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Opening balance	37,420	28,452	36,934	44,518
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Included in net income	797	2,016	801	16,877
Included in OCI	0	0	0	0
Purchases	1,276	15,000	1,758	17,500
Sales	0	(14,749)	0	(48,176)
Settlements/ distributions	0	0	0	0
Closing balance	39,493	30,719	39,493	30,719
Change in unrealized investment gains/(losses)	$ 566	$ 2,502	$ 570	$ 3,936