SEGMENT INFORMATION (DETAILS) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) reportable_segment	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Information [Line Items]
Number of reportable segments | reportable_segment			2
Net premiums earned	$ 941,211	$ 1,000,400	$ 1,845,264	$ 1,946,349
Other insurance related income	3,486	1,683	11,162	4,766
Net losses and loss expenses	(580,153)	(565,829)	(1,092,481)	(1,110,036)
Acquisition costs	(183,263)	(191,862)	(354,805)	(363,899)
General and administrative expenses	(148,482)	(151,081)	(311,723)	(303,810)
Net investment income	88,544	114,867	180,651	197,610
Net realized investment gains (losses)	(11,110)	33,261	(53,662)	43,882
Foreign exchange (losses) gains	(22,108)	(9,705)	41,112	(13,939)
Interest expense and financing costs	(12,939)	(19,975)	(25,196)	(36,569)
Income before income taxes	$ 75,186	$ 211,759	$ 240,322	$ 364,354
Net loss and loss expense ratio	61.60%	56.60%	59.20%	57.00%
Acquisition cost ratio	19.50%	19.20%	19.20%	18.70%
General and administrative expense ratio	15.80%	15.00%	16.90%	15.60%
Combined ratio	96.90%	90.80%	95.30%	91.30%
Goodwill and intangible assets	$ 101,053	$ 90,025	$ 101,053	$ 90,025	$ 88,960
Operating Segments [Member]
Segment Information [Line Items]
Gross premiums written	1,188,413	1,231,279	2,867,345	3,052,678
Net premiums written	946,544	1,000,162	2,402,090	2,664,746
Net premiums earned	941,211	1,000,400	1,845,264	1,946,349
Other insurance related income	3,486	1,683	11,162	4,766
Net losses and loss expenses	(580,153)	(565,829)	(1,092,481)	(1,110,036)
Acquisition costs	(183,263)	(191,862)	(354,805)	(363,899)
General and administrative expenses	(124,433)	(117,811)	(251,502)	(241,834)
Underwriting income (loss)	56,848	126,581	157,638	235,346
Operating Segments [Member] | Insurance [Member]
Segment Information [Line Items]
Gross premiums written	761,126	754,110	1,363,850	1,355,831
Net premiums written	534,263	541,097	971,004	997,789
Net premiums earned	452,322	457,670	899,789	906,884
Other insurance related income	269	0	269	0
Net losses and loss expenses	(297,534)	(290,466)	(583,307)	(569,889)
Acquisition costs	(66,920)	(71,039)	(131,375)	(136,096)
General and administrative expenses	(88,420)	(83,512)	(176,109)	(171,459)
Underwriting income (loss)	$ (283)	$ 12,653	$ 9,267	$ 29,440
Net loss and loss expense ratio	65.80%	63.50%	64.80%	62.80%
Acquisition cost ratio	14.80%	15.50%	14.60%	15.00%
General and administrative expense ratio	19.50%	18.20%	19.60%	19.00%
Combined ratio	100.10%	97.20%	99.00%	96.80%
Goodwill and intangible assets	$ 101,053	$ 90,025	$ 101,053	$ 90,025
Operating Segments [Member] | Reinsurance [Member]
Segment Information [Line Items]
Gross premiums written	427,287	477,169	1,503,495	1,696,847
Net premiums written	412,281	459,065	1,431,086	1,666,957
Net premiums earned	488,889	542,730	945,475	1,039,465
Other insurance related income	3,217	1,683	10,893	4,766
Net losses and loss expenses	(282,619)	(275,363)	(509,174)	(540,147)
Acquisition costs	(116,343)	(120,823)	(223,430)	(227,803)
General and administrative expenses	(36,013)	(34,299)	(75,393)	(70,375)
Underwriting income (loss)	$ 57,131	$ 113,928	$ 148,371	$ 205,906
Net loss and loss expense ratio	57.80%	50.70%	53.90%	52.00%
Acquisition cost ratio	23.80%	22.30%	23.60%	21.90%
General and administrative expense ratio	7.40%	6.30%	8.00%	6.70%
Combined ratio	89.00%	79.30%	85.50%	80.60%
Goodwill and intangible assets	$ 0	$ 0	$ 0	$ 0
Corporate, Non-Segment [Member]
Segment Information [Line Items]
General and administrative expenses	(24,049)	(33,270)	(60,221)	(61,976)
Significant Reconciling Items [Member]
Segment Information [Line Items]
Net investment income	88,544	114,867	180,651	197,610
Net realized investment gains (losses)	(11,110)	33,261	(53,662)	43,882
Foreign exchange (losses) gains	(22,108)	(9,705)	41,112	(13,939)
Interest expense and financing costs	$ (12,939)	$ (19,975)	$ (25,196)	$ (36,569)