INVESTMENTS (Details 3) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
INVESTMENTS
Unrealized losses relative to total invested assets (as a percent)	1.20%
Fair value
Less than 12 months	$ 615,058	$ 88,007
12 Months and Greater	946	960
Total Fair value	616,004	88,967
Cost or amortized Cost
Less than 12 months	638,269	89,232
12 months and greater	957	993
Total Cost or Amortized Cost	639,226	90,225
Unrealized Loss
Less than 12 months	(23,211)	(1,225)
12 Months and Greater	(11)	(33)
Total Unrealized Loss	(23,222)	(1,258)
Cash and Short-term Investments
Cash	87,398	44,314	31,301	81,184
Short-term investments, at cost	22,994	30,462
Maximum
Unrealized Loss
Fair value of trading securities		100
Debt securities
Fair value
Less than 12 months	608,017	71,800
12 Months and Greater	946	960
Total Fair value	608,963	72,760
Cost or amortized Cost
Less than 12 months	630,867	72,150
12 months and greater	957	993
Total Cost or Amortized Cost	631,824	73,143
Unrealized Loss
Less than 12 months	(22,850)	(350)
12 Months and Greater	(11)	(33)
Total Unrealized Loss	(22,861)	(383)
Percent to Total	100.00%
Debt securities | NAIC Rating 1 | AAA/AA/A | Aaa/Aa/A
Fair value
Total Fair value	576,292
Cost or amortized Cost
Total Cost or Amortized Cost	597,964
Unrealized Loss
Total Unrealized Loss	(21,672)
Percent to Total	94.80%
Debt securities | NAIC Rating 2 | BBB | Baa
Fair value
Total Fair value	31,703
Cost or amortized Cost
Total Cost or Amortized Cost	32,870
Unrealized Loss
Total Unrealized Loss	(1,167)
Percent to Total	5.10%
Debt securities | NAIC Rating 3 | BB | Ba
Fair value
Total Fair value	968
Cost or amortized Cost
Total Cost or Amortized Cost	990
Unrealized Loss
Total Unrealized Loss	(22)
Percent to Total	0.10%
U.S. Government
Fair value
Less than 12 months		749
Total Fair value		749
Cost or amortized Cost
Less than 12 months		749
Total Cost or Amortized Cost		749
U.S. Agency
Fair value
Less than 12 months	3,866
Total Fair value	3,866
Cost or amortized Cost
Less than 12 months	3,996
Total Cost or Amortized Cost	3,996
Unrealized Loss
Less than 12 months	(130)
Total Unrealized Loss	(130)
Non-U.S. govt. & agency
Fair value
Less than 12 months	2,985
Total Fair value	2,985
Cost or amortized Cost
Less than 12 months	3,001
Total Cost or Amortized Cost	3,001
Unrealized Loss
Less than 12 months	(16)
Total Unrealized Loss	(16)
Mortgage-backed
Fair value
Less than 12 months	92,321
Total Fair value	92,321
Cost or amortized Cost
Less than 12 months	95,796
Total Cost or Amortized Cost	95,796
Unrealized Loss
Less than 12 months	(3,475)
Total Unrealized Loss	(3,475)
ABS/CMBS
Fair value
Less than 12 months	50,376	18
Total Fair value	50,376	18
Cost or amortized Cost
Less than 12 months	52,101	18
Total Cost or Amortized Cost	52,101	18
Unrealized Loss
Less than 12 months	(1,725)
Total Unrealized Loss	(1,725)
Corporate
Fair value
Less than 12 months	175,314	35,969
12 Months and Greater		960
Total Fair value	175,314	36,929
Cost or amortized Cost
Less than 12 months	182,164	36,162
12 months and greater		993
Total Cost or Amortized Cost	182,164	37,155
Unrealized Loss
Less than 12 months	(6,850)	(193)
12 Months and Greater		(33)
Total Unrealized Loss	(6,850)	(226)
Municipal
Fair value
Less than 12 months	283,155	35,064
12 Months and Greater	946
Total Fair value	284,101	35,064
Cost or amortized Cost
Less than 12 months	293,809	35,221
12 months and greater	957
Total Cost or Amortized Cost	294,766	35,221
Unrealized Loss
Less than 12 months	(10,654)	(157)
12 Months and Greater	(11)
Total Unrealized Loss	(10,665)	(157)
Equity securities
Fair value
Less than 12 months	7,041	16,207
Total Fair value	7,041	16,207
Cost or amortized Cost
Less than 12 months	7,402	17,082
Total Cost or Amortized Cost	7,402	17,082
Unrealized Loss
Less than 12 months	(361)	(875)
Total Unrealized Loss	$ (361)	$ (875)