INVESTMENTS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	$ 1,267,673		$ 1,274,393
Gross unrealized gains	123,289		107,244
Gross unrealized losses	12,358		14,369
Estimated fair value	1,378,604		1,367,268
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	80,204		243,068
Less than twelve months, Unrealized losses	5,253		7,792
Twelve months or longer, Fair value	59,436		73,043
Twelve months or longer, Unrealized losses	7,105		6,577
Total, Fair value	139,640		316,111
Total, Unrealized losses	12,358		14,369
Amortized cost
Due in one year or less	50,535
Due after one year through five years	148,018
Due after five years through ten years	344,710
Due after ten years	435,929
Securities not due at a single maturity date	137,435
Totals	1,116,627		1,130,217
Estimated fair value
Due in one year or less	50,810
Due after one year through five years	155,947
Due after five years through ten years	361,569
Due after ten years	464,071
Securities not due at a single maturity date	133,625
Totals	1,166,022		1,161,025
Realized Investment Gains (Losses) [Abstract]
'Other-than-temporary' impairments	(431)	$ (618)
Net realized investment gains (losses)	(1,085)	783
Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	1,116,627		1,130,217
Gross unrealized gains	58,734		42,885
Gross unrealized losses	9,339		12,077
Estimated fair value	1,166,022		1,161,025
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	56,678		214,736
Less than twelve months, Unrealized losses	2,319		5,661
Twelve months or longer, Fair value	55,017		71,072
Twelve months or longer, Unrealized losses	7,020		6,416
Total, Fair value	111,695		285,808
Total, Unrealized losses	9,339		12,077
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	669	535
Available-for-sale, Gross realized investment losses	(299)	0
US Treasury Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	7,824		12,566
Gross unrealized gains	314		23
Gross unrealized losses	0		0
Estimated fair value	8,138		12,589
US Government-sponsored Enterprises Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	187,366		202,486
Gross unrealized gains	2,145		1,817
Gross unrealized losses	63		1,637
Estimated fair value	189,448		202,666
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	6,987		78,800
Less than twelve months, Unrealized losses	5		1,228
Twelve months or longer, Fair value	11,440		34,079
Twelve months or longer, Unrealized losses	58		409
Total, Fair value	18,427		112,879
Total, Unrealized losses	63		1,637
US States and Political Subdivisions Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	312,476		319,940
Gross unrealized gains	28,304		24,419
Gross unrealized losses	0		0
Estimated fair value	340,780		344,359
Commercial Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	40,098		44,433
Gross unrealized gains	1,661		1,692
Gross unrealized losses	2		17
Estimated fair value	41,757		46,108
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	5,101		6,807
Less than twelve months, Unrealized losses	2		17
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	5,101		6,807
Total, Unrealized losses	2		17
Residential Mortgage Backed Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	93,625		94,279
Gross unrealized gains	2,232		1,059
Gross unrealized losses	7,735		6,795
Estimated fair value	88,122		88,543
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	11,820		22,028
Less than twelve months, Unrealized losses	1,443		1,694
Twelve months or longer, Fair value	23,906		22,781
Twelve months or longer, Unrealized losses	6,292		5,101
Total, Fair value	35,726		44,809
Total, Unrealized losses	7,735		6,795
Collateralized Debt Obligations [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	15,901		17,000
Gross unrealized gains	872		883
Gross unrealized losses	129		39
Estimated fair value	16,644		17,844
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	5,331		6,013
Less than twelve months, Unrealized losses	129		39
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	5,331		6,013
Total, Unrealized losses	129		39
Corporate Debt Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	459,337		439,513
Gross unrealized gains	23,206		12,992
Gross unrealized losses	1,410		3,589
Estimated fair value	481,133		448,916
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	27,439		101,088
Less than twelve months, Unrealized losses	740		2,683
Twelve months or longer, Fair value	19,671		14,212
Twelve months or longer, Unrealized losses	670		906
Total, Fair value	47,110		115,300
Total, Unrealized losses	1,410		3,589
Equity Securities [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	151,046		144,176
Gross unrealized gains	64,555		64,359
Gross unrealized losses	3,019		2,292
Estimated fair value	212,582		206,243
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	23,526		28,332
Less than twelve months, Unrealized losses	2,934		2,131
Twelve months or longer, Fair value	4,419		1,971
Twelve months or longer, Unrealized losses	85		161
Total, Fair value	27,945		30,303
Total, Unrealized losses	3,019		2,292
Realized Investment Gains (Losses) [Abstract]
Available-for-sale, Gross realized investment gains	2,082	2,594
Available-for-sale, Gross realized investment losses	(1,192)	(329)
'Other-than-temporary' impairments	(431)	(618)
Common stocks Financial services [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	26,311		24,557
Gross unrealized gains	7,820		9,731
Gross unrealized losses	688		333
Estimated fair value	33,443		33,955
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	7,858		6,387
Less than twelve months, Unrealized losses	688		333
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	7,858		6,387
Total, Unrealized losses	688		333
Common stocks Information technology [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	18,821		19,427
Gross unrealized gains	9,757		8,807
Gross unrealized losses	59		132
Estimated fair value	28,519		28,102
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,419		1,316
Less than twelve months, Unrealized losses	59		132
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	2,419		1,316
Total, Unrealized losses	59		132
Common stocks Healthcare [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	15,573		15,599
Gross unrealized gains	9,039		10,359
Gross unrealized losses	172		64
Estimated fair value	24,440		25,894
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	2,855		3,199
Less than twelve months, Unrealized losses	172		64
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	2,855		3,199
Total, Unrealized losses	172		64
Common stocks Consumer staples [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,440		11,136
Gross unrealized gains	7,148		7,090
Gross unrealized losses	7		26
Estimated fair value	19,581		18,200
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	89		1,244
Less than twelve months, Unrealized losses	7		26
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	89		1,244
Total, Unrealized losses	7		26
Common stocks Consumer discretionary [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	12,729		10,270
Gross unrealized gains	9,349		8,658
Gross unrealized losses	41		5
Estimated fair value	22,037		18,923
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,094		176
Less than twelve months, Unrealized losses	41		5
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	1,094		176
Total, Unrealized losses	41		5
Common stocks Energy [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	16,815		16,384
Gross unrealized gains	5,596		5,972
Gross unrealized losses	1,821		1,288
Estimated fair value	20,590		21,068
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	5,979		8,233
Less than twelve months, Unrealized losses	1,821		1,272
Twelve months or longer, Fair value	0		116
Twelve months or longer, Unrealized losses	0		16
Total, Fair value	5,979		8,349
Total, Unrealized losses	1,821		1,288
Common stocks Industrials [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	13,942		11,525
Gross unrealized gains	9,697		8,902
Gross unrealized losses	118		11
Estimated fair value	23,521		20,416
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,586		1,263
Less than twelve months, Unrealized losses	118		11
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	1,586		1,263
Total, Unrealized losses	118		11
Common stocks Other [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	16,384		17,246
Gross unrealized gains	5,136		3,672
Gross unrealized losses	28		235
Estimated fair value	21,492		20,683
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	1,646		4,064
Less than twelve months, Unrealized losses	28		235
Twelve months or longer, Fair value	0		0
Twelve months or longer, Unrealized losses	0		0
Total, Fair value	1,646		4,064
Total, Unrealized losses	28		235
Nonredeemable Preferred Stock [Member]
Amortized cost and estimated fair value of available-for-sale securities [Abstract]
Amortized cost	18,031		18,032
Gross unrealized gains	1,013		1,168
Gross unrealized losses	85		198
Estimated fair value	18,959		19,002
Available for sale securities continuous unrealized loss position [Abstract]
Less than twelve months, Fair value	0		2,450
Less than twelve months, Unrealized losses	0		53
Twelve months or longer, Fair value	4,419		1,855
Twelve months or longer, Unrealized losses	85		145
Total, Fair value	4,419		4,305
Total, Unrealized losses	85		$ 198
Other Long-term Investments [Member]
Realized Investment Gains (Losses) [Abstract]
Other long-term investments, net	$ (1,914)	$ (1,399)