SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) reportable_segment	Sep. 30, 2020 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| reportable_segment			2
Segment Information [Line Items]
Net premiums earned	$ 1,211,427	$ 1,091,312	$ 3,472,090	$ 3,283,941
Other insurance related income	7,665	1,440	16,262	(5,270)
Net losses and loss expenses	(911,369)	(879,677)	(2,292,559)	(2,464,012)
Acquisition costs	(231,712)	(230,564)	(669,654)	(697,716)
Underwriting-related general and administrative expenses and corporate expenses	(157,960)	(138,823)	(478,820)	(436,538)
Net investment income	107,339	101,956	326,174	240,098
Net investment gains	10,932	55,609	113,868	45,777
Foreign exchange (losses) gains	28,032	(60,734)	4,316	(8,760)
Interest expense and financing costs	(15,954)	(15,574)	(46,759)	(59,641)
Reorganization expenses	0	(1,413)	0	(822)
Amortization of value of business acquired	(1,028)	(1,028)	(3,083)	(4,111)
Amortization of intangible assets	(3,149)	(2,838)	(9,163)	(8,564)
Income (loss) before income taxes and interest in income of equity method investments	44,223	(80,334)	432,672	(115,618)
Income tax (expense) benefit	(1,186)	12,056	(49,827)	6,030
Interest in income (loss) of equity method investments	11,911	2,896	30,871	(13,579)
Net income (loss)	54,948	(65,382)	413,716	(123,167)
Preferred share dividends	7,563	7,563	22,688	22,688
Net income (loss) available (attributable) to common shareholders	47,385	(72,945)	391,028	(145,855)
Operating Segments
Segment Information [Line Items]
Gross premiums written	1,646,489	1,331,178	6,123,156	5,478,519
Net premiums written	996,471	815,982	3,979,215	3,550,960
Net premiums earned	1,211,427	1,091,312	3,472,090	3,283,941
Other insurance related income	7,665	1,440	16,262	(5,270)
Net losses and loss expenses	(911,369)	(879,677)	(2,292,559)	(2,464,012)
Acquisition costs	(231,712)	(230,564)	(669,654)	(697,716)
Underwriting-related general and administrative expenses and corporate expenses	(134,826)	(117,835)	(396,455)	(361,623)
Underwriting income (loss)	$ (58,815)	$ (135,324)	$ 129,684	$ (244,680)
Net losses and loss expenses ratio (as a percent)	75.20%	80.60%	66.00%	75.00%
Acquisition cost ratio (as a percent)	19.10%	21.10%	19.30%	21.20%
General and administrative expense ratio (as a percent)	13.10%	12.80%	13.80%	13.40%
Combined ratio (as a percent)	107.40%	114.50%	99.10%	109.60%
Goodwill and intangible assets	$ 312,358	$ 324,365	$ 312,358	$ 324,365
Operating Segments \| Insurance
Segment Information [Line Items]
Gross premiums written	1,176,500	935,817	3,548,169	2,914,100
Net premiums written	707,492	544,857	2,128,190	1,729,268
Net premiums earned	681,008	570,184	1,928,970	1,709,268
Other insurance related income	468	688	1,435	2,091
Net losses and loss expenses	(442,681)	(443,389)	(1,131,753)	(1,252,569)
Acquisition costs	(123,529)	(114,569)	(348,172)	(343,579)
Underwriting-related general and administrative expenses and corporate expenses	(104,905)	(94,379)	(307,777)	(284,909)
Underwriting income (loss)	$ 10,361	$ (81,465)	$ 142,703	$ (169,698)
Net losses and loss expenses ratio (as a percent)	65.00%	77.80%	58.70%	73.30%
Acquisition cost ratio (as a percent)	18.10%	20.10%	18.00%	20.10%
General and administrative expense ratio (as a percent)	15.40%	16.50%	16.00%	16.70%
Combined ratio (as a percent)	98.50%	114.40%	92.70%	110.10%
Goodwill and intangible assets	$ 312,358	$ 324,365	$ 312,358	$ 324,365
Operating Segments \| Reinsurance
Segment Information [Line Items]
Gross premiums written	469,989	395,361	2,574,987	2,564,419
Net premiums written	288,979	271,125	1,851,025	1,821,692
Net premiums earned	530,419	521,128	1,543,120	1,574,673
Other insurance related income	7,197	752	14,827	(7,361)
Net losses and loss expenses	(468,688)	(436,288)	(1,160,806)	(1,211,443)
Acquisition costs	(108,183)	(115,995)	(321,482)	(354,137)
Underwriting-related general and administrative expenses and corporate expenses	(29,921)	(23,456)	(88,678)	(76,714)
Underwriting income (loss)	$ (69,176)	$ (53,859)	$ (13,019)	$ (74,982)
Net losses and loss expenses ratio (as a percent)	88.40%	83.70%	75.20%	76.90%
Acquisition cost ratio (as a percent)	20.40%	22.30%	20.80%	22.50%
General and administrative expense ratio (as a percent)	5.60%	4.50%	5.80%	4.90%
Combined ratio (as a percent)	114.40%	110.50%	101.80%	104.30%
Goodwill and intangible assets	$ 0	$ 0	$ 0	$ 0
Segment Reconciling Items
Segment Information [Line Items]
Net investment income	107,339	101,956	326,174	240,098
Net investment gains	10,932	55,609	113,868	45,777
Foreign exchange (losses) gains	28,032	(60,734)	4,316	(8,760)
Interest expense and financing costs	(15,954)	(15,574)	(46,759)	(59,641)
Reorganization expenses	0	(1,413)	0	(822)
Amortization of value of business acquired	(1,028)	(1,028)	(3,083)	(4,111)
Amortization of intangible assets	(3,149)	(2,838)	(9,163)	(8,564)
Corporate Expenses
Segment Information [Line Items]
Underwriting-related general and administrative expenses and corporate expenses	$ (23,134)	$ (20,988)	$ (82,365)	$ (74,915)

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.