SEGMENT INFORMATION (DETAILS) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Information [Line Items]
Number of reportable segments			2
Gross premiums written	$ 1,014,375	$ 1,046,163	$ 2,539,545	$ 2,594,593
Net premiums written	801,575	850,139	2,168,762	2,250,919
Net premiums earned	850,603	840,014	1,696,968	1,628,215
Other insurance related income	299	126	931	889
Net losses and loss expenses	(467,637)	(564,959)	(978,328)	(1,584,759)
Acquisition costs	(156,397)	(147,905)	(324,793)	(283,262)
General and administrative expenses	(107,129)	(98,302)	(212,347)	(193,415)
Underwriting income (loss)	119,739	28,974	182,431	(432,332)
Corporate expenses	(54,202)	(19,803)	(72,637)	(41,210)
Net investment income	74,449	100,018	190,472	210,673
Net realized investment gains	30,405	37,477	44,896	67,621
Foreign exchange (losses) gains	36,162	(18,517)	15,715	(33,575)
Interest expense and financing costs	(15,170)	(15,445)	(30,807)	(31,305)
Income (loss) before income taxes	191,383	112,704	330,070	(260,128)
Net loss and loss expense ratio	55.00%	67.30%	57.70%	97.30%
Acquisition cost ratio	18.40%	17.60%	19.10%	17.40%
General and administrative expense ratio	18.90%	14.00%	16.80%	14.40%
Combined ratio	92.30%	98.90%	93.60%	129.10%
Goodwill and intangible assets	98,203	103,404	98,203	103,404	99,590
Insurance [Member]
Segment Information [Line Items]
Gross premiums written	675,009	682,097	1,199,689	1,107,088
Net premiums written	465,238	495,049	843,853	784,365
Net premiums earned	386,580	359,875	776,837	687,523
Other insurance related income	299	126	931	889
Net losses and loss expenses	(225,900)	(218,219)	(467,623)	(484,852)
Acquisition costs	(58,654)	(51,244)	(119,808)	(93,322)
General and administrative expenses	(77,770)	(70,229)	(155,214)	(137,956)
Underwriting income (loss)	24,555	20,309	35,123	(27,718)
Net loss and loss expense ratio	58.40%	60.60%	60.20%	70.50%
Acquisition cost ratio	15.20%	14.30%	15.40%	13.60%
General and administrative expense ratio	20.10%	19.50%	20.00%	20.10%
Combined ratio	93.70%	94.40%	95.60%	104.20%
Goodwill and intangible assets	98,203	103,404	98,203	103,404
Reinsurance [Member]
Segment Information [Line Items]
Gross premiums written	339,366	364,066	1,339,856	1,487,505
Net premiums written	336,337	355,090	1,324,909	1,466,554
Net premiums earned	464,023	480,139	920,131	940,692
Other insurance related income	0	0	0	0
Net losses and loss expenses	(241,737)	(346,740)	(510,705)	(1,099,907)
Acquisition costs	(97,743)	(96,661)	(204,985)	(189,940)
General and administrative expenses	(29,359)	(28,073)	(57,133)	(55,459)
Underwriting income (loss)	95,184	8,665	147,308	(404,614)
Net loss and loss expense ratio	52.10%	72.20%	55.50%	116.90%
Acquisition cost ratio	21.10%	20.10%	22.30%	20.20%
General and administrative expense ratio	6.30%	5.90%	6.20%	5.90%
Combined ratio	79.50%	98.20%	84.00%	143.00%
Goodwill and intangible assets	0	0	0	0
Unallocated To Segment [Member]
Segment Information [Line Items]
Corporate expenses	(54,202)	(19,803)	(72,637)	(41,210)
Net investment income	74,449	100,018	190,472	210,673
Net realized investment gains	30,405	37,477	44,896	67,621
Foreign exchange (losses) gains	36,162	(18,517)	15,715	(33,575)
Interest expense and financing costs	$ (15,170)	$ (15,445)	$ (30,807)	$ (31,305)