INVESTMENTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	$ 1,282,314		$ 1,282,314		$ 1,203,978
Gross unrealized gains	102,305		102,305		128,038
Gross unrealized losses	12,353		12,353		7,481
Estimated fair value	1,372,266		1,372,266		1,324,535
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	177,974		177,974		74,394
Less than twelve months, Unrealized losses	7,039		7,039		2,142
Twelve months or longer, Fair value	70,876		70,876		152,526
Twelve months or longer, Unrealized losses	5,314		5,314		5,339
Total, Fair value	248,850		248,850		226,920
Total, Unrealized losses	12,353		12,353		7,481
Amortized cost
Due in one year or less	66,429		66,429
Due after one year through five years	144,462		144,462
Due after five years through ten years	280,923		280,923
Due after ten years	507,529		507,529
Securities not due at a single maturity date	140,030		140,030
Totals	1,139,373		1,139,373		1,080,006
Estimated fair value
Due in one year or less	67,150		67,150
Due after one year through five years	152,924		152,924
Due after five years through ten years	286,725		286,725
Due after ten years	533,372		533,372
Securities not due at a single maturity date	137,790		137,790
Totals	1,177,961		1,177,961		1,127,499
Realized Investment Gains (Losses) [Abstract]
'Other-than-temporary' impairments	(628)	$ (561)	(1,293)	$ (877)
Net realized investment gains	7,498	(390)	11,555	3,215
Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	1,139,373		1,139,373		1,080,006
Gross unrealized gains	47,652		47,652		54,148
Gross unrealized losses	9,064		9,064		6,655
Estimated fair value	1,177,961		1,177,961		1,127,499
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	136,195		136,195		65,655
Less than twelve months, Unrealized losses	3,982		3,982		1,633
Twelve months or longer, Fair value	69,043		69,043		150,623
Twelve months or longer, Unrealized losses	5,082		5,082		5,022
Total, Fair value	205,238		205,238		216,278
Total, Unrealized losses	9,064		9,064		6,655
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	61	129	642	495
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	9,600		9,600		9,574
Gross unrealized gains	137		137		129
Gross unrealized losses	0		0		0
Estimated fair value	9,737		9,737		9,703
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	221,466		221,466		215,425
Gross unrealized gains	2,743		2,743		2,313
Gross unrealized losses	744		744		2,122
Estimated fair value	223,465		223,465		215,616
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	44,495		44,495		24,473
Less than twelve months, Unrealized losses	471		471		94
Twelve months or longer, Fair value	35,212		35,212		97,446
Twelve months or longer, Unrealized losses	273		273		2,028
Total, Fair value	79,707		79,707		121,919
Total, Unrealized losses	744		744		2,122
US States and Political Subdivisions Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	319,666		319,666		299,258
Gross unrealized gains	24,270		24,270		26,840
Gross unrealized losses	0		0		40
Estimated fair value	343,936		343,936		326,058
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value					0
Less than twelve months, Unrealized losses					0
Twelve months or longer, Fair value					3,757
Twelve months or longer, Unrealized losses					40
Total, Fair value					3,757
Total, Unrealized losses					40
Commercial Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	41,304		41,304		42,996
Gross unrealized gains	2,437		2,437		3,766
Gross unrealized losses	2		2		0
Estimated fair value	43,739		43,739		46,762
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	579		579		1,102
Less than twelve months, Unrealized losses	2		2		0
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	579		579		1,102
Total, Unrealized losses	2		2		0
Residential Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	94,411		94,411		100,296
Gross unrealized gains	1,660		1,660		1,402
Gross unrealized losses	6,387		6,387		3,745
Estimated fair value	89,684		89,684		97,953
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	15,102		15,102		21,451
Less than twelve months, Unrealized losses	1,873		1,873		1,252
Twelve months or longer, Fair value	22,393		22,393		21,163
Twelve months or longer, Unrealized losses	4,514		4,514		2,493
Total, Fair value	37,495		37,495		42,614
Total, Unrealized losses	6,387		6,387		3,745
Collateralized Debt Obligations [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	17,738		17,738		14,798
Gross unrealized gains	1,066		1,066		1,213
Gross unrealized losses	66		66		6
Estimated fair value	18,738		18,738		16,005
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	6,136		6,136		1,889
Less than twelve months, Unrealized losses	66		66		6
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	6,136		6,136		1,889
Total, Unrealized losses	66		66		6
Corporate Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	435,188		435,188		397,659
Gross unrealized gains	15,339		15,339		18,485
Gross unrealized losses	1,865		1,865		742
Estimated fair value	448,662		448,662		415,402
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	69,883		69,883		16,740
Less than twelve months, Unrealized losses	1,570		1,570		281
Twelve months or longer, Fair value	11,438		11,438		28,257
Twelve months or longer, Unrealized losses	295		295		461
Total, Fair value	81,321		81,321		44,997
Total, Unrealized losses	1,865		1,865		742
Equity Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	142,941		142,941		123,972
Gross unrealized gains	54,653		54,653		73,890
Gross unrealized losses	3,289		3,289		826
Estimated fair value	194,305		194,305		197,036
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	41,779		41,779		8,739
Less than twelve months, Unrealized losses	3,057		3,057		509
Twelve months or longer, Fair value	1,833		1,833		1,903
Twelve months or longer, Unrealized losses	232		232		317
Total, Fair value	43,612		43,612		10,642
Total, Unrealized losses	3,289		3,289		826
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	3,345	1,140	11,681	6,456
Available-for-sale, Gross realized investment losses	(2,525)	(181)	(3,278)	(662)
'Other-than-temporary' impairments	(628)	(561)	(1,293)	(877)
Common stocks Financial services [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	27,143		27,143		22,586
Gross unrealized gains	8,215		8,215		11,835
Gross unrealized losses	839		839		42
Estimated fair value	34,519		34,519		34,379
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	9,754		9,754		1,162
Less than twelve months, Unrealized losses	831		831		9
Twelve months or longer, Fair value	57		57		187
Twelve months or longer, Unrealized losses	8		8		33
Total, Fair value	9,811		9,811		1,349
Total, Unrealized losses	839		839		42
Common stocks Information technology [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	18,956		18,956		15,755
Gross unrealized gains	7,845		7,845		11,110
Gross unrealized losses	237		237		0
Estimated fair value	26,564		26,564		26,865
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,552		3,552
Less than twelve months, Unrealized losses	237		237
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	3,552		3,552
Total, Unrealized losses	237		237
Common stocks Healthcare [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,969		14,969		14,673
Gross unrealized gains	9,388		9,388		12,179
Gross unrealized losses	239		239		0
Estimated fair value	24,118		24,118		26,852
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,388		3,388
Less than twelve months, Unrealized losses	239		239
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	3,388		3,388
Total, Unrealized losses	239		239
Common stocks Consumer staples [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	10,093		10,093		10,584
Gross unrealized gains	5,762		5,762		6,112
Gross unrealized losses	86		86		2
Estimated fair value	15,769		15,769		16,694
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,762		1,762		1,051
Less than twelve months, Unrealized losses	86		86		2
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	1,762		1,762		1,051
Total, Unrealized losses	86		86		2
Common stocks Consumer discretionary [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	10,471		10,471		11,304
Gross unrealized gains	8,705		8,705		11,420
Gross unrealized losses	26		26		33
Estimated fair value	19,150		19,150		22,691
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	371		371		822
Less than twelve months, Unrealized losses	26		26		33
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	371		371		822
Total, Unrealized losses	26		26		33
Common stocks Energy [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	16,927		16,927		15,837
Gross unrealized gains	4,999		4,999		7,458
Gross unrealized losses	756		756		432
Estimated fair value	21,170		21,170		22,863
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	9,478		9,478		4,298
Less than twelve months, Unrealized losses	756		756		432
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	9,478		9,478		4,298
Total, Unrealized losses	756		756		432
Common stocks Industrials [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	11,153		11,153		9,658
Gross unrealized gains	6,924		6,924		8,596
Gross unrealized losses	332		332		33
Estimated fair value	17,745		17,745		18,221
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,501		3,501		1,406
Less than twelve months, Unrealized losses	332		332		33
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	3,501		3,501		1,406
Total, Unrealized losses	332		332		33
Common stocks Other [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	15,243		15,243		11,493
Gross unrealized gains	2,269		2,269		4,563
Gross unrealized losses	509		509		0
Estimated fair value	17,003		17,003		16,056
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	7,510		7,510
Less than twelve months, Unrealized losses	509		509
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	7,510		7,510
Total, Unrealized losses	509		509
Nonredeemable Preferred Stock [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	17,986		17,986		12,082
Gross unrealized gains	546		546		617
Gross unrealized losses	265		265		284
Estimated fair value	18,267		18,267		12,415
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,463		2,463		0
Less than twelve months, Unrealized losses	41		41		0
Twelve months or longer, Fair value	1,776		1,776		1,716
Twelve months or longer, Unrealized losses	224		224		284
Total, Fair value	4,239		4,239		1,716
Total, Unrealized losses	265		265		$ 284
Other Long-term Investments [Member]
Realized Investment Gains (Losses) [Abstract]
Other long-term investments, net	$ 7,245	$ (917)	$ 3,803	$ (2,105)