This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities, the change in fair value of investment-related derivatives not designated as hedges and any hedge ineffectiveness recognized in earnings in relation to investment portfolio-related fair value hedges.

No definition available.

SEGMENT INFORMATION - Segment results (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) reportable_segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| reportable_segment									2
Segment Information [Line Items]
Gross premiums written									$ 6,826,938	$ 6,898,858	$ 6,910,065
Net premiums written									4,336,409	4,489,615	4,658,962
Net premiums earned	$ 1,087,368	$ 1,091,312	$ 1,104,003	$ 1,088,625	$ 1,172,051	$ 1,157,307	$ 1,123,607	$ 1,134,212	4,371,309	4,587,178	4,791,495
Other insurance related income (loss)									(8,089)	16,444	10,622
Net losses and loss expenses									(3,281,252)	(3,044,798)	(3,190,287)
Acquisition costs									(929,517)	(1,024,582)	(968,835)
Underwriting-related general and administrative expenses									(579,790)	(634,831)	(627,389)
Underwriting income (loss)	(80,835)	(135,324)	87,412	(196,767)	(49,254)	(78,718)	78,659	77,822
Net investment income	109,503	101,956	45,040	93,101	117,557	115,763	137,949	107,303	349,601	478,572	438,507
Net investment gains	83,356	55,609	53,043	(62,877)	42,712	14,527	21,225	12,767	129,133	91,233	(150,218)
Foreign exchange losses									(81,069)	12,041	29,165
Interest expense and financing costs									(75,049)	(68,107)	(67,432)
Reorganization expenses									(7,881)	(37,384)	(66,940)
Amortization of value of business acquired	(1,000)	(1,000)	(1,000)	(2,000)	(2,000)	(4,000)	(7,000)	(13,000)	(5,139)	(26,722)	(172,332)
Amortization of intangible assets									(11,390)	(11,597)	(13,814)
Income (loss) before income taxes and interest in income (loss) of equity method investments									(129,133)	337,447	12,542
Goodwill and intangible assets	324,288								324,288
Operating Segments
Segment Information [Line Items]
Gross premiums written									6,826,938	6,898,858	6,910,065
Net premiums written									4,336,409	4,489,615	4,658,962
Net premiums earned									4,371,309	4,587,178	4,791,495
Other insurance related income (loss)									(8,089)	16,444	10,622
Net losses and loss expenses									(3,281,252)	(3,044,798)	(3,190,287)
Acquisition costs									(929,517)	(1,024,582)	(968,835)
Underwriting-related general and administrative expenses									(477,968)	(505,735)	(519,168)
Underwriting income (loss)									$ (325,517)	$ 28,507	$ 123,827
Net losses and loss expenses ratio									75.10%	66.40%	66.60%
Acquisition cost ratio									21.30%	22.30%	20.20%
General and administrative expense ratio									13.20%	13.90%	13.10%
Combined ratio									109.60%	102.60%	99.90%
Goodwill and intangible assets	320,434				332,553				$ 320,434	$ 332,553	$ 343,571
Operating Segments \| Insurance
Segment Information [Line Items]
Gross premiums written									4,018,399	3,675,931	3,797,592
Net premiums written									2,357,501	2,209,155	2,324,747
Net premiums earned									2,299,038	2,190,084	2,362,606
Other insurance related income (loss)									2,647	2,858	3,460
Net losses and loss expenses									(1,697,014)	(1,278,679)	(1,494,323)
Acquisition costs									(461,533)	(468,281)	(399,193)
Underwriting-related general and administrative expenses									(378,839)	(401,963)	(395,252)
Underwriting income (loss)									$ (235,701)	$ 44,019	$ 77,298
Net losses and loss expenses ratio									73.80%	58.40%	63.20%
Acquisition cost ratio									20.10%	21.40%	16.90%
General and administrative expense ratio									16.50%	18.30%	16.80%
Combined ratio									110.40%	98.10%	96.90%
Goodwill and intangible assets	320,434				332,553				$ 320,434	$ 332,553	$ 343,571
Operating Segments \| Reinsurance
Segment Information [Line Items]
Gross premiums written									2,808,539	3,222,927	3,112,473
Net premiums written									1,978,908	2,280,460	2,334,215
Net premiums earned									2,072,271	2,397,094	2,428,889
Other insurance related income (loss)									(10,736)	13,586	7,162
Net losses and loss expenses									(1,584,238)	(1,766,119)	(1,695,964)
Acquisition costs									(467,984)	(556,301)	(569,642)
Underwriting-related general and administrative expenses									(99,129)	(103,772)	(123,916)
Underwriting income (loss)									$ (89,816)	$ (15,512)	$ 46,529
Net losses and loss expenses ratio									76.40%	73.70%	69.80%
Acquisition cost ratio									22.60%	23.20%	23.50%
General and administrative expense ratio									4.80%	4.30%	5.10%
Combined ratio									103.80%	101.20%	98.40%
Goodwill and intangible assets	0				0				$ 0	$ 0	$ 0
Significant Reconciling Items
Segment Information [Line Items]
Net investment income									349,601	478,572	438,507
Net investment gains									129,133	91,233	(150,218)
Foreign exchange losses									(81,069)	12,041	29,165
Interest expense and financing costs									(75,049)	(68,107)	(67,432)
Reorganization expenses									(7,881)	(37,384)	(66,940)
Amortization of value of business acquired									(5,139)	(26,722)	(172,332)
Amortization of intangible assets									(11,390)	(11,597)	(13,814)
Corporate
Segment Information [Line Items]
Underwriting-related general and administrative expenses	$ (27,000)	$ (21,000)	$ (27,000)	$ (27,000)	$ (32,000)	$ (29,000)	$ (32,000)	$ (36,000)	$ (101,822)	$ (129,096)	$ (108,221)