INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 15,466
Due after one year through five years	240,318
Due after five years through 10 years	571,095
Due after 10 years	278,993
Total amoritzed cost	1,476,063
Fair Value
Due in one year or less	15,604
Due after one year through five years	249,737
Due after five years through 10 years	592,340
Due after 10 years	289,642
Total fair value	1,529,559	1,495,087
Fair value measured on recurring basis | Significant Unobservable Inputs (Level 3)
INVESTMENTS
Total assets at fair value	0
Debt securities
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	1,476,063	1,448,204
Gross Unrealized Gains	57,631	53,004
Gross Unrealized Losses	(4,135)	(6,121)
Fair Value	1,529,559	1,495,087
U.S. government
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	33,313	33,668
Gross Unrealized Gains	279	131
Gross Unrealized Losses		(11)
Fair Value	33,592	33,788
U.S. Agency
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	13,498	6,385
Gross Unrealized Gains	554	362
Fair Value	14,052	6,747
Non-U.S. govt. & agency
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	1,892	9,862
Gross Unrealized Gains	125	803
Fair Value	2,017	10,665
ABS/CMBS
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	125,847	133,894
Gross Unrealized Gains	2,298	1,821
Gross Unrealized Losses	(223)	(411)
Fair Value	127,922	135,304
Agency MBS
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	244,344	256,443
Gross Unrealized Gains	10,480	9,401
Gross Unrealized Losses	(510)	(1,376)
Fair Value	254,314	264,468
Corporate
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	593,814	543,183
Gross Unrealized Gains	25,378	23,697
Gross Unrealized Losses	(3,130)	(4,190)
Fair Value	616,062	562,690
Municipal
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	463,355	464,769
Gross Unrealized Gains	18,517	16,789
Gross Unrealized Losses	(272)	(133)
Fair Value	481,600	481,425
Mtge/ABS/CMBS
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	370,191
Fair Value	382,236
Equity securities
Available-for-sale
Available-for-sale Securities, Amortized Cost Basis, Total	191,993	193,535
Gross Unrealized Gains	200,630	218,105
Gross Unrealized Losses	(960)	(998)
Fair Value	$ 391,663	$ 410,642