SEGMENT INFORMATION (Detail) - Net premiums earned by line of business (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
P&C Operations:
P&C Operations	$ 5,327,112		$ 5,031,137		$ 5,151,739
Life Operations:
Life Operations	363,018		382,924		555,101
Total	5,690,130		5,414,061		5,706,840
Casualty Professional Lines [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	1,287,230		1,316,172		1,276,005
Casualty Professional Lines [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	213,949		222,720		196,624
Casualty Professional Lines [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Casualty Professional Lines [Member]
P&C Operations:
P&C Operations	1,501,179		1,538,892		1,472,629
Casualty Other Lines [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	695,094		611,674		655,126
Casualty Other Lines [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	256,853		219,154		257,610
Casualty Other Lines [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Casualty Other Lines [Member]
P&C Operations:
P&C Operations	951,947		830,828		912,736
Property Catastrophe [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	0		0		2,396
Property Catastrophe [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	387,523		323,588		312,780
Property Catastrophe [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Property Catastrophe [Member]
P&C Operations:
P&C Operations	387,523		323,588		315,176
Other Property [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	481,148		416,806		424,045
Other Property [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	587,611		534,422		560,379
Other Property [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Other Property [Member]
P&C Operations:
P&C Operations	1,068,759		951,228		984,424
Marine, Energy, Aviation and Satellite [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	528,454		540,319		546,806
Marine, Energy, Aviation and Satellite [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	130,855		88,855		83,532
Marine, Energy, Aviation and Satellite [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Marine, Energy, Aviation and Satellite [Member]
P&C Operations:
P&C Operations	659,309		629,174		630,338
Other Speciality Lines | Insurance Segment [Member]
P&C Operations:
P&C Operations	665,727	[1]	621,839	[1]	634,436	[1]
Other Speciality Lines | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	0	[1]	0	[1]	0	[1]
Other Speciality Lines | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0	[1]	0	[1]	0	[1]
Other Speciality Lines
P&C Operations:
P&C Operations	665,727	[1]	621,839	[1]	634,436	[1]
Other Lines [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	3,552	[2]	7,577	[2]	12,217	[2]
Other Lines [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	90,776	[2]	112,303	[2]	172,588	[2]
Other Lines [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0	[2]	0	[2]	0	[2]
Other Lines [Member]
P&C Operations:
P&C Operations	94,328	[2]	119,880	[2]	184,805	[2]
Structured Indemnity [Member] | Insurance Segment [Member]
P&C Operations:
P&C Operations	2,522		14,751		8,762
Structured Indemnity [Member] | Reinsurance Segment [Member]
P&C Operations:
P&C Operations	(4,182)		957		8,433
Structured Indemnity [Member] | Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Structured Indemnity [Member]
P&C Operations:
P&C Operations	(1,660)		15,708		17,195
Insurance Segment [Member] | Other Life [Member]
Life Operations:
Life Operations	0		0		0
Insurance Segment [Member] | Annuity [Member]
Life Operations:
Life Operations	0		0		0
Insurance Segment [Member]
P&C Operations:
P&C Operations	3,663,727		3,529,138		3,559,793
Life Operations:
Life Operations	0		0		0
Total	3,663,727		3,529,138		3,559,793
Reinsurance Segment [Member] | Other Life [Member]
Life Operations:
Life Operations	0		0		0
Reinsurance Segment [Member] | Annuity [Member]
Life Operations:
Life Operations	0		0		0
Reinsurance Segment [Member]
P&C Operations:
P&C Operations	1,663,385		1,501,999		1,591,946
Life Operations:
Life Operations	0		0		0
Total	1,663,385		1,501,999		1,591,946
Life Operations Segment [Member] | Other Life [Member]
Life Operations:
Life Operations	230,786		255,905		422,594
Life Operations Segment [Member] | Annuity [Member]
Life Operations:
Life Operations	132,232		127,019		132,507
Life Operations Segment [Member]
P&C Operations:
P&C Operations	0		0		0
Life Operations:
Life Operations	363,018		382,924		555,101
Total	363,018		382,924		555,101
Other Life [Member]
Life Operations:
Life Operations	230,786		255,905		422,594
Annuity [Member]
Life Operations:
Life Operations	$ 132,232		$ 127,019		$ 132,507

[1] Other specialty lines within the Insurance segment includes: environmental, programs, equine, warranty, specie, middle markets and excess and surplus lines.

[2] Other includes credit and surety, whole account contracts and other lines.