INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	$ 1,116,120		$ 1,123,407
Gross unrealized gains	105,025		98,434
Gross unrealized losses	15,470		24,009
Estimated fair value	1,205,675		1,197,832
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	264,860		318,108
Twelve months or longer, Fair value	55,475		43,692
Total, Fair value	320,335		361,800
Less than twelve months, Unrealized losses	9,998		18,717
Twelve months or longer, Unrealized losses	5,472		5,292
Total, Unrealized losses	15,470		24,009
Amortized cost
Due in one year or less	14,861
Due after one year through five years	204,579
Due after five years through ten years	148,790
Due after ten years	480,347
Mortgage-backed securities	150,074
Totals	998,651
Estimated fair value
Due in one year or less	15,163
Due after one year through five years	217,051
Due after five years through ten years	153,719
Due after ten years	490,599
Mortgage-backed securities	153,469
Totals	1,030,001		1,027,984
Realized Investment Gains (Losses) [Abstract]
'Other-than-temporary' impairments	(316)	(21)
Net realized investment gains (losses)	1,262	2,668
Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	998,651		1,009,572
Gross unrealized gains	45,867		41,236
Gross unrealized losses	14,517		22,824
Estimated fair value	1,030,001		1,027,984
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	253,746		308,972
Twelve months or longer, Fair value	53,839		42,208
Total, Fair value	307,585		351,180
Less than twelve months, Unrealized losses	9,409		18,048
Twelve months or longer, Unrealized losses	5,108		4,776
Total, Unrealized losses	14,517		22,824
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	81	686
Available-for-sale, Gross realized investment losses	(92)	0
US Treasury Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,548		9,540
Gross unrealized gains	173		191
Gross unrealized losses	197		319
Estimated fair value	9,524		9,412
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	4,632		4,507
Twelve months or longer, Fair value	0		0
Total, Fair value	4,632		4,507
Less than twelve months, Unrealized losses	197		319
Twelve months or longer, Unrealized losses	0		0
Total, Unrealized losses	197		319
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	154,289		156,981
Gross unrealized gains	1,442		1,356
Gross unrealized losses	8,043		11,391
Estimated fair value	147,688		146,946
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	71,839		93,856
Twelve months or longer, Fair value	32,169		24,053
Total, Fair value	104,008		117,909
Less than twelve months, Unrealized losses	4,902		8,120
Twelve months or longer, Unrealized losses	3,141		3,271
Total, Unrealized losses	8,043		11,391
US States and Political Subdivisions Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	342,900		346,554
Gross unrealized gains	19,344		15,040
Gross unrealized losses	1,876		4,542
Estimated fair value	360,368		357,052
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	53,336		74,523
Twelve months or longer, Fair value	5,481		3,008
Total, Fair value	58,817		77,531
Less than twelve months, Unrealized losses	1,631		4,335
Twelve months or longer, Unrealized losses	245		207
Total, Unrealized losses	1,876		4,542
Commercial Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	54,168		63,185
Gross unrealized gains	5,189		5,842
Gross unrealized losses	0		88
Estimated fair value	59,357		68,939
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value			10,551
Twelve months or longer, Fair value			0
Total, Fair value			10,551
Less than twelve months, Unrealized losses			88
Twelve months or longer, Unrealized losses			0
Total, Unrealized losses			88
Residential Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	95,906		96,058
Gross unrealized gains	826		1,073
Gross unrealized losses	2,620		2,952
Estimated fair value	94,112		94,179
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	60,790		44,243
Twelve months or longer, Fair value	5,551		4,600
Total, Fair value	66,341		48,843
Less than twelve months, Unrealized losses	1,588		2,482
Twelve months or longer, Unrealized losses	1,032		470
Total, Unrealized losses	2,620		2,952
Collateralized Debt Obligations [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	10,341		11,456
Gross unrealized gains	1,184		1,192
Gross unrealized losses	0		0
Estimated fair value	11,525		12,648
Corporate Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	331,499		325,798
Gross unrealized gains	17,709		16,542
Gross unrealized losses	1,781		3,532
Estimated fair value	347,427		338,808
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	63,149		81,292
Twelve months or longer, Fair value	10,638		10,547
Total, Fair value	73,787		91,839
Less than twelve months, Unrealized losses	1,091		2,704
Twelve months or longer, Unrealized losses	690		828
Total, Unrealized losses	1,781		3,532
Equity Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	117,469		113,835
Gross unrealized gains	59,158		57,198
Gross unrealized losses	953		1,185
Estimated fair value	175,674		169,848
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	11,114		9,136
Twelve months or longer, Fair value	1,636		1,484
Total, Fair value	12,750		10,620
Less than twelve months, Unrealized losses	589		669
Twelve months or longer, Unrealized losses	364		516
Total, Unrealized losses	953		1,185
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	2,033	2,091
Available-for-sale, Gross realized investment losses	(76)	(88)
'Other-than-temporary' impairments	(316)	(21)
Common stocks Financial services [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	19,345		19,273
Gross unrealized gains	9,409		9,374
Gross unrealized losses	53		149
Estimated fair value	28,701		28,498
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,530		2,801
Twelve months or longer, Fair value	0		0
Total, Fair value	1,530		2,801
Less than twelve months, Unrealized losses	53		149
Twelve months or longer, Unrealized losses	0		0
Total, Unrealized losses	53		149
Common stocks Information technology [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	17,198		12,645
Gross unrealized gains	6,765		6,301
Gross unrealized losses	103		29
Estimated fair value	23,860		18,917
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	4,144		610
Twelve months or longer, Fair value	0		0
Total, Fair value	4,144		610
Less than twelve months, Unrealized losses	103		29
Twelve months or longer, Unrealized losses	0		0
Total, Unrealized losses	103		29
Common stocks Healthcare [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,570		12,801
Gross unrealized gains	10,710		9,144
Gross unrealized losses	0		0
Estimated fair value	23,280		21,945
Common stocks Consumer staples [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	9,502		9,162
Gross unrealized gains	4,160		3,849
Gross unrealized losses	0		0
Estimated fair value	13,662		13,011
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value			30
Twelve months or longer, Fair value			0
Total, Fair value			30
Less than twelve months, Unrealized losses			0
Twelve months or longer, Unrealized losses			0
Total, Unrealized losses			0
Common stocks Consumer discretionary [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	10,690		10,722
Gross unrealized gains	10,270		10,309
Gross unrealized losses	0		0
Estimated fair value	20,960		21,031
Common stocks Energy [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	14,882		14,102
Gross unrealized gains	6,912		7,341
Gross unrealized losses	267		326
Estimated fair value	21,527		21,117
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	730		1,450
Twelve months or longer, Fair value	0		0
Total, Fair value	730		1,450
Less than twelve months, Unrealized losses	267		326
Twelve months or longer, Unrealized losses	0		0
Total, Unrealized losses	267		326
Common stocks Industrials [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	8,386		11,190
Gross unrealized gains	6,207		6,075
Gross unrealized losses	0		1
Estimated fair value	14,593		17,264
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	38		625
Twelve months or longer, Fair value	0		0
Total, Fair value	38		625
Less than twelve months, Unrealized losses	0		1
Twelve months or longer, Unrealized losses	0		0
Total, Unrealized losses	0		1
Common stocks Other [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,814		13,358
Gross unrealized gains	4,262		4,489
Gross unrealized losses	157		36
Estimated fair value	16,919		17,811
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,431		1,499
Twelve months or longer, Fair value	0		0
Total, Fair value	2,431		1,499
Less than twelve months, Unrealized losses	157		36
Twelve months or longer, Unrealized losses	0		0
Total, Unrealized losses	157		36
Nonredeemable Preferred Stock [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,082		10,582
Gross unrealized gains	463		316
Gross unrealized losses	373		644
Estimated fair value	12,172		10,254
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,241		2,121
Twelve months or longer, Fair value	1,636		1,484
Total, Fair value	3,877		3,605
Less than twelve months, Unrealized losses	9		128
Twelve months or longer, Unrealized losses	364		516
Total, Unrealized losses	373		644
Other Long-term Investments [Member]
Realized Investment Gains (Losses) [Abstract]
Other long-term investments, Gross realized investment losses	$ (368)	$ 0