FAIR VALUE MEASUREMENTS (Detail) - Additional information about assets and liabilities measured at fair value on a recurring basis (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Corporate [Member]
Balance, beginning of period	$ 36,866	$ 10,311
Realized gains (losses)	(276)	(7,257)
Movement in unrealized gains (losses)	92	1,748
Purchases and issuances	14,840	20,328
Sales and settlements	(10,049)	(2,164)
Transfers into Level 3	2,105	14,749
Transfers out of Level 3	(19,760)	(849)
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	23,818	36,866
Movement in total gains (losses) above relating to instruments still held at the reporting date	92	1,964
Residential Mortgage-Backed Securities Agency [Member]
Balance, beginning of period	30,255	7,894
Realized gains (losses)	(11)	(360)
Movement in unrealized gains (losses)	(145)	(74)
Purchases and issuances	6,176	30,689
Sales and settlements	(4,186)	0
Transfers into Level 3	2,655	0
Transfers out of Level 3	(2,703)	(7,894)
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	32,041	30,255
Movement in total gains (losses) above relating to instruments still held at the reporting date	(156)	(74)
Residential Mortgage-Backed Securities Non-Agency [Member]
Balance, beginning of period	4,964	42,190
Realized gains (losses)	0	(1,452)
Movement in unrealized gains (losses)	0	306
Purchases and issuances	0	0
Sales and settlements	0	(2,226)
Transfers into Level 3	0	5,601
Transfers out of Level 3	(4,964)	(39,455)
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	0	4,964
Movement in total gains (losses) above relating to instruments still held at the reporting date	0	(28)
Commercial mortgage-backed securities [Member]
Balance, beginning of period	1,623	2,755
Realized gains (losses)	0	(908)
Movement in unrealized gains (losses)	0	1,062
Purchases and issuances	0	0
Sales and settlements	0	(685)
Transfers into Level 3	0	0
Transfers out of Level 3	(1,623)	0
Fixed maturities to short-term investments classification change	0	(601)
Balance, end of period	0	1,623
Movement in total gains (losses) above relating to instruments still held at the reporting date	0	223
Collateralized Debt Obligations [Member]
Balance, beginning of period	721,572	197,149
Realized gains (losses)	(3,458)	(28,253)
Movement in unrealized gains (losses)	2,404	120,932
Purchases and issuances	2,379	0
Sales and settlements	(68,165)	(7,525)
Transfers into Level 3	1,886	471,211
Transfers out of Level 3	(5,767)	(59)
Fixed maturities to short-term investments classification change	0	(31,883)
Balance, end of period	650,851	721,572
Movement in total gains (losses) above relating to instruments still held at the reporting date	(6,431)	117,764
Other Asset Backed Securities [Member]
Balance, beginning of period	24,650	38,179
Realized gains (losses)	(849)	(18,107)
Movement in unrealized gains (losses)	6,896	14,685
Purchases and issuances	0	4,356
Sales and settlements	(9,114)	(1,504)
Transfers into Level 3	0	1,355
Transfers out of Level 3	(5,031)	(14,314)
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	16,552	24,650
Movement in total gains (losses) above relating to instruments still held at the reporting date	12,334	8,747
Non US Sovereign Government Supranational And Government Related [Member]
Balance, beginning of period	3,667	3,217
Realized gains (losses)	0	0
Movement in unrealized gains (losses)	0	34
Purchases and issuances	0	0
Sales and settlements	0	0
Transfers into Level 3	0	416
Transfers out of Level 3	(3,667)	0
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	0	3,667
Movement in total gains (losses) above relating to instruments still held at the reporting date	0	34
Short-term Investments [Member]
Balance, beginning of period	0	0
Realized gains (losses)	0	0
Movement in unrealized gains (losses)	0	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	0	0
Movement in total gains (losses) above relating to instruments still held at the reporting date	0	0
Other Investments [Member]
Balance, beginning of period	133,717	75,584
Realized gains (losses)	11,592	3,677
Movement in unrealized gains (losses)	14,108	14,461
Purchases and issuances	12,177	15,443
Sales and settlements	(57,635)	(26,180)
Transfers into Level 3	0	18,248
Transfers out of Level 3	0	0
Fixed maturities to short-term investments classification change	0	32,484
Balance, end of period	113,959	133,717
Movement in total gains (losses) above relating to instruments still held at the reporting date	23,391	14,286
Derivative Contracts [Member]
Balance, beginning of period	(39,195)	100,515
Realized gains (losses)	0	874
Movement in unrealized gains (losses)	(3,173)	57,688
Purchases and issuances	0	(198,272)
Sales and settlements	(276)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fixed maturities to short-term investments classification change	0	0
Balance, end of period	(42,644)	(39,195)
Movement in total gains (losses) above relating to instruments still held at the reporting date	$ (3,173)	$ 57,688