INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	$ 1,182,584		$ 1,182,584		$ 1,123,407
Gross unrealized gains	114,925		114,925		98,434
Gross unrealized losses	8,886		8,886		24,009
Estimated fair value	1,288,623		1,288,623		1,197,832
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	132,948		132,948		318,108
Less than twelve months, Unrealized losses	1,834		1,834		18,717
Twelve months or longer, Fair value	153,528		153,528		43,692
Twelve months or longer, Unrealized losses	7,052		7,052		5,292
Total, Fair value	286,476		286,476		361,800
Total, Unrealized losses	8,886		8,886		24,009
Amortized cost
Due in one year or less	23,233		23,233
Due after one year through five years	200,474		200,474
Due after five years through ten years	187,845		187,845
Due after ten years	500,162		500,162
Mortgage-backed securities	147,884		147,884
Totals	1,059,598		1,059,598		1,009,572
Estimated fair value
Due in one year or less	23,647		23,647
Due after one year through five years	212,084		212,084
Due after five years through ten years	193,274		193,274
Due after ten years	522,136		522,136
Mortgage-backed securities	150,099		150,099
Totals	1,101,240		1,101,240		1,027,984
Realized Investment Gains (Losses) [Abstract]
'Other-than-temporary' impairments	(561)	(3)	(877)	(24)
Net realized investment gains (losses)	(390)	1,007	3,215	3,850
Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	1,059,598		1,059,598		1,009,572
Gross unrealized gains	49,986		49,986		41,236
Gross unrealized losses	8,344		8,344		22,824
Estimated fair value	1,101,240		1,101,240		1,027,984
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	124,739		124,739		308,972
Less than twelve months, Unrealized losses	1,561		1,561		18,048
Twelve months or longer, Fair value	151,797		151,797		42,208
Twelve months or longer, Unrealized losses	6,783		6,783		4,776
Total, Fair value	276,536		276,536		351,180
Total, Unrealized losses	8,344		8,344		22,824
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	129	44	495	862
Available-for-sale, Gross realized investment losses	0	0	(92)	(725)
US Treasury Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,565		9,565		9,540
Gross unrealized gains	132		132		191
Gross unrealized losses	99		99		319
Estimated fair value	9,598		9,598		9,412
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	0		0		4,507
Less than twelve months, Unrealized losses	0		0		319
Twelve months or longer, Fair value	4,739		4,739		0
Twelve months or longer, Unrealized losses	99		99		0
Total, Fair value	4,739		4,739		4,507
Total, Unrealized losses	99		99		319
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	206,743		206,743		156,981
Gross unrealized gains	1,781		1,781		1,356
Gross unrealized losses	4,161		4,161		11,391
Estimated fair value	204,363		204,363		146,946
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	32,507		32,507		93,856
Less than twelve months, Unrealized losses	112		112		8,120
Twelve months or longer, Fair value	95,617		95,617		24,053
Twelve months or longer, Unrealized losses	4,049		4,049		3,271
Total, Fair value	128,124		128,124		117,909
Total, Unrealized losses	4,161		4,161		11,391
US States and Political Subdivisions Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	307,807		307,807		346,554
Gross unrealized gains	24,373		24,373		15,040
Gross unrealized losses	87		87		4,542
Estimated fair value	332,093		332,093		357,052
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	0		0		74,523
Less than twelve months, Unrealized losses	0		0		4,335
Twelve months or longer, Fair value	3,715		3,715		3,008
Twelve months or longer, Unrealized losses	87		87		207
Total, Fair value	3,715		3,715		77,531
Total, Unrealized losses	87		87		4,542
Commercial Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	47,513		47,513		63,185
Gross unrealized gains	4,180		4,180		5,842
Gross unrealized losses	0		0		88
Estimated fair value	51,693		51,693		68,939
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value					10,551
Less than twelve months, Unrealized losses					88
Twelve months or longer, Fair value					0
Twelve months or longer, Unrealized losses					0
Total, Fair value					10,551
Total, Unrealized losses					88
Residential Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	100,371		100,371		96,058
Gross unrealized gains	992		992		1,073
Gross unrealized losses	2,957		2,957		2,952
Estimated fair value	98,406		98,406		94,179
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	42,877		42,877		44,243
Less than twelve months, Unrealized losses	1,027		1,027		2,482
Twelve months or longer, Fair value	23,215		23,215		4,600
Twelve months or longer, Unrealized losses	1,930		1,930		470
Total, Fair value	66,092		66,092		48,843
Total, Unrealized losses	2,957		2,957		2,952
Collateralized Debt Obligations [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,811		14,811		11,456
Gross unrealized gains	1,176		1,176		1,192
Gross unrealized losses	50		50		0
Estimated fair value	15,937		15,937		12,648
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	4,987		4,987
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	4,987		4,987
Total, Unrealized losses	50		50
Corporate Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	372,788		372,788		325,798
Gross unrealized gains	17,352		17,352		16,542
Gross unrealized losses	990		990		3,532
Estimated fair value	389,150		389,150		338,808
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	44,368		44,368		81,292
Less than twelve months, Unrealized losses	372		372		2,704
Twelve months or longer, Fair value	24,511		24,511		10,547
Twelve months or longer, Unrealized losses	618		618		828
Total, Fair value	68,879		68,879		91,839
Total, Unrealized losses	990		990		3,532
Equity Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	122,986		122,986		113,835
Gross unrealized gains	64,939		64,939		57,198
Gross unrealized losses	542		542		1,185
Estimated fair value	187,383		187,383		169,848
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	8,209		8,209		9,136
Less than twelve months, Unrealized losses	273		273		669
Twelve months or longer, Fair value	1,731		1,731		1,484
Twelve months or longer, Unrealized losses	269		269		516
Total, Fair value	9,940		9,940		10,620
Total, Unrealized losses	542		542		1,185
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	1,140	968	6,456	4,292
Available-for-sale, Gross realized investment losses	(181)	(2)	(662)	(555)
'Other-than-temporary' impairments	(561)	(3)	(877)	(24)
Common stocks Financial services [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	20,136		20,136		19,273
Gross unrealized gains	9,888		9,888		9,374
Gross unrealized losses	66		66		149
Estimated fair value	29,958		29,958		28,498
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,184		2,184		2,801
Less than twelve months, Unrealized losses	66		66		149
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	2,184		2,184		2,801
Total, Unrealized losses	66		66		149
Common stocks Information technology [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	16,898		16,898		12,645
Gross unrealized gains	9,514		9,514		6,301
Gross unrealized losses	0		0		29
Estimated fair value	26,412		26,412		18,917
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value					610
Less than twelve months, Unrealized losses					29
Twelve months or longer, Fair value					0
Twelve months or longer, Unrealized losses					0
Total, Fair value					610
Total, Unrealized losses					29
Common stocks Healthcare [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,008		14,008		12,801
Gross unrealized gains	11,003		11,003		9,144
Gross unrealized losses	8		8		0
Estimated fair value	25,003		25,003		21,945
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	840		840
Less than twelve months, Unrealized losses	8		8
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	840		840
Total, Unrealized losses	8		8
Common stocks Consumer staples [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,985		9,985		9,162
Gross unrealized gains	4,739		4,739		3,849
Gross unrealized losses	0		0		0
Estimated fair value	14,724		14,724		13,011
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value					30
Less than twelve months, Unrealized losses					0
Twelve months or longer, Fair value					0
Twelve months or longer, Unrealized losses					0
Total, Fair value					30
Total, Unrealized losses					0
Common stocks Consumer discretionary [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,886		9,886		10,722
Gross unrealized gains	9,353		9,353		10,309
Gross unrealized losses	0		0		0
Estimated fair value	19,239		19,239		21,031
Common stocks Energy [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	16,638		16,638		14,102
Gross unrealized gains	8,094		8,094		7,341
Gross unrealized losses	111		111		326
Estimated fair value	24,621		24,621		21,117
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,078		3,078		1,450
Less than twelve months, Unrealized losses	111		111		326
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	3,078		3,078		1,450
Total, Unrealized losses	111		111		326
Common stocks Industrials [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	8,386		8,386		11,190
Gross unrealized gains	7,462		7,462		6,075
Gross unrealized losses	20		20		1
Estimated fair value	15,828		15,828		17,264
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	351		351		625
Less than twelve months, Unrealized losses	20		20		1
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	351		351		625
Total, Unrealized losses	20		20		1
Common stocks Other [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,967		14,967		13,358
Gross unrealized gains	4,377		4,377		4,489
Gross unrealized losses	68		68		36
Estimated fair value	19,276		19,276		17,811
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,756		1,756		1,499
Less than twelve months, Unrealized losses	68		68		36
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	1,756		1,756		1,499
Total, Unrealized losses	68		68		36
Nonredeemable Preferred Stock [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,082		12,082		10,582
Gross unrealized gains	509		509		316
Gross unrealized losses	269		269		644
Estimated fair value	12,322		12,322		10,254
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	0		0		2,121
Less than twelve months, Unrealized losses	0		0		128
Twelve months or longer, Fair value	1,731		1,731		1,484
Twelve months or longer, Unrealized losses	269		269		516
Total, Fair value	1,731		1,731		3,605
Total, Unrealized losses	269		269		644
Other Long-term Investments [Member]
Realized Investment Gains (Losses) [Abstract]
Other long-term investments, Gross realized investment losses	$ (917)	$ 0	$ (2,105)	$ 0