INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 12,910
Due after one year through five years	146,264
Due after five years through 10 years	616,368
Due after 10 years	242,961
Total	1,359,943
Fair Value
Due in one year or less	13,014
Due after one year through five years	155,143
Due after five years through 10 years	627,254
Due after 10 years	238,030
Total	1,379,012	1,378,582
Fair value measured on recurring basis | Significant Unobservable Inputs (Level 3)
INVESTMENTS
Total assets at fair value	0
Fixed income securities
Available-for-sale
Cost or Amortized Cost	1,359,943	1,294,350
Gross Unrealized Gains	41,930	84,615
Gross Unrealized Losses	(22,861)	(383)
Fair Value	1,379,012	1,378,582
U.S. agency
Available-for-sale
Cost or Amortized Cost	8,537	11,609
Gross Unrealized Gains	52	150
Gross Unrealized Losses	(130)
Fair Value	8,459	11,759
Corporate
Available-for-sale
Cost or Amortized Cost	474,628	535,437
Gross Unrealized Gains	23,746	45,497
Gross Unrealized Losses	(6,850)	(226)
Fair Value	491,524	580,708
Mortgage-backed
Available-for-sale
Cost or Amortized Cost	247,317	234,629
Gross Unrealized Gains	7,722	15,758
Gross Unrealized Losses	(3,475)
Fair Value	251,564	250,387
ABS/CMBS
Available-for-sale
Cost or Amortized Cost	94,123	72,681
Gross Unrealized Gains	1,609	4,648
Gross Unrealized Losses	(1,725)
Fair Value	94,007	77,329
Non-U.S. govt. & agency
Available-for-sale
Cost or Amortized Cost	11,414	8,410
Gross Unrealized Gains	469	957
Gross Unrealized Losses	(16)
Fair Value	11,867	9,367
U.S. government
Available-for-sale
Cost or Amortized Cost	17,090	16,358
Gross Unrealized Gains	253	355
Fair Value	17,343	16,713
Municipal
Available-for-sale
Cost or Amortized Cost	506,834	415,226
Gross Unrealized Gains	8,079	17,250
Gross Unrealized Losses	(10,665)	(157)
Fair Value	504,248	432,319
Mtge/ABS/CMBS
Amortized Cost
Total	341,440
Fair Value
Total	345,571
Equity securities
Available-for-sale
Cost or Amortized Cost	218,656	240,287
Gross Unrealized Gains	173,861	136,376
Gross Unrealized Losses	(361)	(875)
Fair Value	$ 392,156	$ 375,788