INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	$ 1,148,899		$ 1,148,899		$ 1,123,407
Gross unrealized gains	116,190		116,190		98,434
Gross unrealized losses	9,310		9,310		24,009
Estimated fair value	1,255,779		1,255,779		1,197,832
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	59,037		59,037		318,108
Less than twelve months, Unrealized losses	1,145		1,145		18,717
Twelve months or longer, Fair value	207,901		207,901		43,692
Twelve months or longer, Unrealized losses	8,165		8,165		5,292
Total, Fair value	266,938		266,938		361,800
Total, Unrealized losses	9,310		9,310		24,009
Amortized cost
Due in one year or less	14,324		14,324
Due after one year through five years	209,948		209,948
Due after five years through ten years	166,906		166,906
Due after ten years	487,249		487,249
Mortgage-backed securities	149,602		149,602
Totals	1,028,029		1,028,029		1,009,572
Estimated fair value
Due in one year or less	14,582		14,582
Due after one year through five years	223,617		223,617
Due after five years through ten years	173,341		173,341
Due after ten years	506,834		506,834
Mortgage-backed securities	152,829		152,829
Totals	1,071,203		1,071,203		1,027,984
Realized Investment Gains (Losses) [Abstract]
'Other-than-temporary' impairments	0	0	(316)	(21)
Net realized investment gains (losses)	2,343	175	3,605	2,843
Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	1,028,029		1,028,029		1,009,572
Gross unrealized gains	52,207		52,207		41,236
Gross unrealized losses	9,033		9,033		22,824
Estimated fair value	1,071,203		1,071,203		1,027,984
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	57,248		57,248		308,972
Less than twelve months, Unrealized losses	1,117		1,117		18,048
Twelve months or longer, Fair value	206,151		206,151		42,208
Twelve months or longer, Unrealized losses	7,916		7,916		4,776
Total, Fair value	263,399		263,399		351,180
Total, Unrealized losses	9,033		9,033		22,824
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	285	132	366	818
Available-for-sale, Gross realized investment losses	0	(725)	(92)	(725)
US Treasury Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,556		9,556		9,540
Gross unrealized gains	157		157		191
Gross unrealized losses	98		98		319
Estimated fair value	9,615		9,615		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	4,736		4,736		0
Twelve months or longer, Unrealized losses	98		98		0
Total, Fair value	4,736		4,736		4,507
Total, Unrealized losses	98		98		319
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	188,583		188,583		156,981
Gross unrealized gains	1,875		1,875		1,356
Gross unrealized losses	4,977		4,977		11,391
Estimated fair value	185,481		185,481		146,946
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	12,638		12,638		93,856
Less than twelve months, Unrealized losses	47		47		8,120
Twelve months or longer, Fair value	102,022		102,022		24,053
Twelve months or longer, Unrealized losses	4,930		4,930		3,271
Total, Fair value	114,660		114,660		117,909
Total, Unrealized losses	4,977		4,977		11,391
US States and Political Subdivisions Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	319,885		319,885		346,554
Gross unrealized gains	23,196		23,196		15,040
Gross unrealized losses	580		580		4,542
Estimated fair value	342,501		342,501		357,052
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	3,445		3,445		74,523
Less than twelve months, Unrealized losses	10		10		4,335
Twelve months or longer, Fair value	41,566		41,566		3,008
Twelve months or longer, Unrealized losses	570		570		207
Total, Fair value	45,011		45,011		77,531
Total, Unrealized losses	580		580		4,542
Commercial Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	50,708		50,708		63,185
Gross unrealized gains	4,886		4,886		5,842
Gross unrealized losses	0		0		88
Estimated fair value	55,594		55,594		68,939
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	344		344		10,551
Less than twelve months, Unrealized losses	0		0		88
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	344		344		10,551
Total, Unrealized losses	0		0		88
Residential Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	98,894		98,894		96,058
Gross unrealized gains	987		987		1,073
Gross unrealized losses	2,646		2,646		2,952
Estimated fair value	97,235		97,235		94,179
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	24,586		24,586		44,243
Less than twelve months, Unrealized losses	973		973		2,482
Twelve months or longer, Fair value	25,938		25,938		4,600
Twelve months or longer, Unrealized losses	1,673		1,673		470
Total, Fair value	50,524		50,524		48,843
Total, Unrealized losses	2,646		2,646		2,952
Collateralized Debt Obligations [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	10,306		10,306		11,456
Gross unrealized gains	1,258		1,258		1,192
Gross unrealized losses	0		0		0
Estimated fair value	11,564		11,564		12,648
Corporate Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	350,097		350,097		325,798
Gross unrealized gains	19,848		19,848		16,542
Gross unrealized losses	732		732		3,532
Estimated fair value	369,213		369,213		338,808
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	16,235		16,235		81,292
Less than twelve months, Unrealized losses	87		87		2,704
Twelve months or longer, Fair value	31,889		31,889		10,547
Twelve months or longer, Unrealized losses	645		645		828
Total, Fair value	48,124		48,124		91,839
Total, Unrealized losses	732		732		3,532
Equity Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	120,870		120,870		113,835
Gross unrealized gains	63,983		63,983		57,198
Gross unrealized losses	277		277		1,185
Estimated fair value	184,576		184,576		169,848
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,789		1,789		9,136
Less than twelve months, Unrealized losses	28		28		669
Twelve months or longer, Fair value	1,750		1,750		1,484
Twelve months or longer, Unrealized losses	249		249		516
Total, Fair value	3,539		3,539		10,620
Total, Unrealized losses	277		277		1,185
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	3,283	1,233	5,316	3,324
Available-for-sale, Gross realized investment losses	(405)	(465)	(481)	(553)
'Other-than-temporary' impairments	0	0	(316)	(21)
Common stocks Financial services [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	21,346		21,346		19,273
Gross unrealized gains	10,374		10,374		9,374
Gross unrealized losses	19		19		149
Estimated fair value	31,701		31,701		28,498
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	265		265		2,801
Less than twelve months, Unrealized losses	19		19		149
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	265		265		2,801
Total, Unrealized losses	19		19		149
Common stocks Information technology [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	15,666		15,666		12,645
Gross unrealized gains	8,279		8,279		6,301
Gross unrealized losses	0		0		29
Estimated fair value	23,945		23,945		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	12,516		12,516		12,801
Gross unrealized gains	9,783		9,783		9,144
Gross unrealized losses	1		1		0
Estimated fair value	22,298		22,298		21,945
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value		65		65
Less than twelve months, Unrealized losses		1		1
Twelve months or longer, Fair value		0		0
Twelve months or longer, Unrealized losses		0		0
Total, Fair value		65		65
Total, Unrealized losses		1		1
Common stocks Consumer staples [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,189		9,189		9,162
Gross unrealized gains	4,285		4,285		3,849
Gross unrealized losses	0		0		0
Estimated fair value	13,474		13,474		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	10,478		10,478		10,722
Gross unrealized gains	10,298		10,298		10,309
Gross unrealized losses	0		0		0
Estimated fair value	20,776		20,776		21,031
Common stocks Energy [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	17,879		17,879		14,102
Gross unrealized gains	9,261		9,261		7,341
Gross unrealized losses	3		3		326
Estimated fair value	27,137		27,137		21,117
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,315		1,315		1,450
Less than twelve months, Unrealized losses	3		3		326
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	1,315		1,315		1,450
Total, Unrealized losses	3		3		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	6,423		6,423		6,075
Gross unrealized losses	4		4		1
Estimated fair value	14,805		14,805		17,264
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	118		118		625
Less than twelve months, Unrealized losses	4		4		1
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	118		118		625
Total, Unrealized losses	4		4		1
Common stocks Other [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	13,328		13,328		13,358
Gross unrealized gains	4,620		4,620		4,489
Gross unrealized losses	1		1		36
Estimated fair value	17,947		17,947		17,811
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	26		26		1,499
Less than twelve months, Unrealized losses	1		1		36
Twelve months or longer, Fair value	0		0		0
Twelve months or longer, Unrealized losses	0		0		0
Total, Fair value	26		26		1,499
Total, Unrealized losses	1		1		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	660		660		316
Gross unrealized losses	249		249		644
Estimated fair value	12,493		12,493		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	1,750		1,750		1,484
Twelve months or longer, Unrealized losses	249		249		516
Total, Fair value	1,750		1,750		3,605
Total, Unrealized losses	249		249		644
Other Long-term Investments [Member]
Realized Investment Gains (Losses) [Abstract]
Other long-term investments, Gross realized investment losses	$ (820)	$ 0	$ (1,188)	$ 0