INVESTMENTS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	$ 1,257,503		$ 1,257,503		$ 1,203,978
Gross unrealized gains	109,475		109,475		128,038
Gross unrealized losses	12,730		12,730		7,481
Estimated fair value	1,354,248		1,354,248		1,324,535
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	335,447		335,447		74,394
Less than twelve months, Unrealized losses	6,753		6,753		2,142
Twelve months or longer, Fair value	67,052		67,052		152,526
Twelve months or longer, Unrealized losses	5,977		5,977		5,339
Total, Fair value	402,499		402,499		226,920
Total, Unrealized losses	12,730		12,730		7,481
Amortized cost
Due in one year or less	42,908		42,908
Due after one year through five years	173,108		173,108
Due after five years through ten years	255,605		255,605
Due after ten years	512,514		512,514
Mortgage-backed securities	138,324		138,324
Totals	1,122,459		1,122,459		1,080,006
Estimated fair value
Due in one year or less	43,353		43,353
Due after one year through five years	182,650		182,650
Due after five years through ten years	259,396		259,396
Due after ten years	532,158		532,158
Mortgage-backed securities	137,405		137,405
Totals	1,154,962		1,154,962		1,127,499
Realized Investment Gains (Losses) [Abstract]
'Other-than-temporary' impairments	(47)	$ 0	(665)	$ (316)
Net realized investment gains	3,274	2,343	4,057	3,605
Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	1,122,459		1,122,459		1,080,006
Gross unrealized gains	43,661		43,661		54,148
Gross unrealized losses	11,158		11,158		6,655
Estimated fair value	1,154,962		1,154,962		1,127,499
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	308,096		308,096		65,655
Less than twelve months, Unrealized losses	5,404		5,404		1,633
Twelve months or longer, Fair value	65,160		65,160		150,623
Twelve months or longer, Unrealized losses	5,754		5,754		5,022
Total, Fair value	373,256		373,256		216,278
Total, Unrealized losses	11,158		11,158		6,655
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	46	285	581	366
Available-for-sale, Gross realized investment losses	0	0	0	(92)
US Treasury Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,591		9,591		9,574
Gross unrealized gains	62		62		129
Gross unrealized losses	15		15		0
Estimated fair value	9,638		9,638		9,703
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	4,837		4,837
Less than twelve months, Unrealized losses	15		15
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	4,837		4,837
Total, Unrealized losses	15		15
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	227,144		227,144		215,425
Gross unrealized gains	2,058		2,058		2,313
Gross unrealized losses	3,890		3,890		2,122
Estimated fair value	225,312		225,312		215,616
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	111,562		111,562		24,473
Less than twelve months, Unrealized losses	2,076		2,076		94
Twelve months or longer, Fair value	33,669		33,669		97,446
Twelve months or longer, Unrealized losses	1,814		1,814		2,028
Total, Fair value	145,231		145,231		121,919
Total, Unrealized losses	3,890		3,890		2,122
US States and Political Subdivisions Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	306,533		306,533		299,258
Gross unrealized gains	21,335		21,335		26,840
Gross unrealized losses	475		475		40
Estimated fair value	327,393		327,393		326,058
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	45,475		45,475		0
Less than twelve months, Unrealized losses	475		475		0
Twelve months or longer, Fair value	0		0		3,757
Twelve months or longer, Unrealized losses	0		0		40
Total, Fair value	45,475		45,475		3,757
Total, Unrealized losses	475		475		40
Commercial Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	42,365		42,365		42,996
Gross unrealized gains	2,798		2,798		3,766
Gross unrealized losses	7		7		0
Estimated fair value	45,156		45,156		46,762
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,176		3,176		1,102
Less than twelve months, Unrealized losses	7		7		0
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	3,176		3,176		1,102
Total, Unrealized losses	7		7		0
Residential Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	95,959		95,959		100,296
Gross unrealized gains	1,110		1,110		1,402
Gross unrealized losses	4,820		4,820		3,745
Estimated fair value	92,249		92,249		97,953
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	24,612		24,612		21,451
Less than twelve months, Unrealized losses	988		988		1,252
Twelve months or longer, Fair value	21,853		21,853		21,163
Twelve months or longer, Unrealized losses	3,832		3,832		2,493
Total, Fair value	46,465		46,465		42,614
Total, Unrealized losses	4,820		4,820		3,745
Collateralized Debt Obligations [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	13,583		13,583		14,798
Gross unrealized gains	1,053		1,053		1,213
Gross unrealized losses	37		37		6
Estimated fair value	14,599		14,599		16,005
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	6,175		6,175		1,889
Less than twelve months, Unrealized losses	37		37		6
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	6,175		6,175		1,889
Total, Unrealized losses	37		37		6
Corporate Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	427,284		427,284		397,659
Gross unrealized gains	15,245		15,245		18,485
Gross unrealized losses	1,914		1,914		742
Estimated fair value	440,615		440,615		415,402
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	112,259		112,259		16,740
Less than twelve months, Unrealized losses	1,806		1,806		281
Twelve months or longer, Fair value	9,638		9,638		28,257
Twelve months or longer, Unrealized losses	108		108		461
Total, Fair value	121,897		121,897		44,997
Total, Unrealized losses	1,914		1,914		742
Equity Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	135,044		135,044		123,972
Gross unrealized gains	65,814		65,814		73,890
Gross unrealized losses	1,572		1,572		826
Estimated fair value	199,286		199,286		197,036
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	27,351		27,351		8,739
Less than twelve months, Unrealized losses	1,349		1,349		509
Twelve months or longer, Fair value	1,892		1,892		1,903
Twelve months or longer, Unrealized losses	223		223		317
Total, Fair value	29,243		29,243		10,642
Total, Unrealized losses	1,572		1,572		826
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	5,742	3,283	8,336	5,316
Available-for-sale, Gross realized investment losses	(424)	(405)	(753)	(481)
'Other-than-temporary' impairments	(47)	0	(665)	(316)
Common stocks Financial services [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	26,103		26,103		22,586
Gross unrealized gains	10,390		10,390		11,835
Gross unrealized losses	204		204		42
Estimated fair value	36,289		36,289		34,379
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	4,095		4,095		1,162
Less than twelve months, Unrealized losses	202		202		9
Twelve months or longer, Fair value	62		62		187
Twelve months or longer, Unrealized losses	2		2		33
Total, Fair value	4,157		4,157		1,349
Total, Unrealized losses	204		204		42
Common stocks Information technology [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	17,467		17,467		15,755
Gross unrealized gains	9,425		9,425		11,110
Gross unrealized losses	56		56		0
Estimated fair value	26,836		26,836		26,865
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	959		959
Less than twelve months, Unrealized losses	56		56
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	959		959
Total, Unrealized losses	56		56
Common stocks Healthcare [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,204		14,204		14,673
Gross unrealized gains	12,117		12,117		12,179
Gross unrealized losses	50		50		0
Estimated fair value	26,271		26,271		26,852
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,940		1,940
Less than twelve months, Unrealized losses	50		50
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	1,940		1,940
Total, Unrealized losses	50		50
Common stocks Consumer staples [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	8,860		8,860		10,584
Gross unrealized gains	5,509		5,509		6,112
Gross unrealized losses	34		34		2
Estimated fair value	14,335		14,335		16,694
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	405		405		1,051
Less than twelve months, Unrealized losses	34		34		2
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	405		405		1,051
Total, Unrealized losses	34		34		2
Common stocks Consumer discretionary [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,716		12,716		11,304
Gross unrealized gains	12,048		12,048		11,420
Gross unrealized losses	32		32		33
Estimated fair value	24,732		24,732		22,691
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	877		877		822
Less than twelve months, Unrealized losses	32		32		33
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	877		877		822
Total, Unrealized losses	32		32		33
Common stocks Energy [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	16,897		16,897		15,837
Gross unrealized gains	6,634		6,634		7,458
Gross unrealized losses	638		638		432
Estimated fair value	22,893		22,893		22,863
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	6,709		6,709		4,298
Less than twelve months, Unrealized losses	629		629		432
Twelve months or longer, Fair value	42		42		0
Twelve months or longer, Unrealized losses	9		9		0
Total, Fair value	6,751		6,751		4,298
Total, Unrealized losses	638		638		432
Common stocks Industrials [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	13,462		13,462		9,658
Gross unrealized gains	7,051		7,051		8,596
Gross unrealized losses	220		220		33
Estimated fair value	20,293		20,293		18,221
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	5,938		5,938		1,406
Less than twelve months, Unrealized losses	220		220		33
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	5,938		5,938		1,406
Total, Unrealized losses	220		220		33
Common stocks Other [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	10,749		10,749		11,493
Gross unrealized gains	2,148		2,148		4,563
Gross unrealized losses	104		104		0
Estimated fair value	12,793		12,793		16,056
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,947		3,947
Less than twelve months, Unrealized losses	104		104
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	3,947		3,947
Total, Unrealized losses	104		104
Nonredeemable Preferred Stock [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,586		14,586		12,082
Gross unrealized gains	492		492		617
Gross unrealized losses	234		234		284
Estimated fair value	14,844		14,844		12,415
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,481		2,481		0
Less than twelve months, Unrealized losses	22		22		0
Twelve months or longer, Fair value	1,788		1,788		1,716
Twelve months or longer, Unrealized losses	212		212		284
Total, Fair value	4,269		4,269		1,716
Total, Unrealized losses	234		234		$ 284
Other Long-term Investments [Member]
Realized Investment Gains (Losses) [Abstract]
Other long-term investments, Gross realized investment losses	$ (2,043)	$ (820)	$ (3,442)	$ (1,188)