Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013 Security	Mar. 31, 2012	Dec. 31, 2012 Security
Schedule of Available-For-Sale Securities [Line Items]
Fair Value			$ 553,251
Cost or Amortized Cost			498,686
Gross Unrealized Gains			57,502
Gross Unrealized Losses			(2,937)
Net Unrealized Gains (losses)			54,565
Applicable federal income taxes	(19,578)		(19,098)
Net unrealized gains - net of tax	36,358		35,467
Number of other than temporarily impaired securities	6		5
Number of other than temporarily impaired securities loss recognized in accumulated other comprehensive income	4		4
Available-for-sale securities continuous unrealized loss position [Abstract]
Number of Securities, total	254		259
Available-for-sale securities continuous unrealized loss position, Fair Value [Abstract]
Fair value, total	104,647		123,485
Available-for-sale securities continuous unrealized loss position, aggregate losses [Abstract]
Gross unrealized loss, total	(2,476)		(2,937)
Available-for-sale securities debt maturities fair value [Abstract]
One year or less, Fair Value	145,477
Excess of one year to five years, Fair Value	207,061
Excess of five years to ten years, Fair Value	28,331
Excess of ten years, Fair Value	2,584
Total maturities, Fair Value	383,453
Asset-backed securities	49,168
Available-for-sale securities debt securities current	432,621
Available-for-sale securities debt maturities amortized cost basis [Abstract]
One year or less, Amortized Cost Basis	144,847
Excess of one year to five years, Amortized Cost Basis	205,716
Excess of five years to ten years, Amortized Cost Basis	27,851
Excess of ten years, Amortized Cost Basis	2,423
Total maturities, Amortized Cost Basis	380,837
Asset-backed securities	46,821
Available-for-sale securities debt maturities amortized cost basis, Total	427,658
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Limited partnerships - net gain (loss)	3,713		5,420
Totals	14,347	5,381	5,381
Available for sale securities gain loss activity [Abstract]
Realized net gains (losses) on the disposal of securities	9,244		(96)
Mark-to-market adjustment	210		57
Equity in gains of limited partnership investments - realized and unrealized	3,713		5,420
Write-downs based upon objective criteria	(6)		0
Recovery of prior write-downs upon sale or disposal	1,186		0
Totals	14,347	5,381	5,381
Net unrealized gain on investments	2,733
Net unrealized gains in limited partnership	7,173
Undistributed earnings of limited partnership, net of taxes	22,114
U.S. government obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	75,562		70,742
Cost or Amortized Cost	75,575		70,720
Gross Unrealized Gains	81		43
Gross Unrealized Losses	(94)		(21)
Net Unrealized Gains (losses)	(13)		22
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	23,190		25,040
Cost or Amortized Cost	21,611		23,954
Gross Unrealized Gains	1,692		1,218
Gross Unrealized Losses	(113)		(132)
Net Unrealized Gains (losses)	1,579		1,086
Commercial mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	12,444		11,828
Cost or Amortized Cost	11,663		11,006
Gross Unrealized Gains	806		849
Gross Unrealized Losses	(25)		(27)
Net Unrealized Gains (losses)	781		822
States and municipal obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	179,854		194,865
Cost or Amortized Cost	179,180		194,258
Gross Unrealized Gains	784		757
Gross Unrealized Losses	(110)		(150)
Net Unrealized Gains (losses)	674		607
Corporate securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	119,717		120,596
Cost or Amortized Cost	117,988		118,574
Gross Unrealized Gains	2,861		2,923
Gross Unrealized Losses	(1,132)		(901)
Net Unrealized Gains (losses)	1,729		2,022
Foreign government obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	21,854		22,598
Cost or Amortized Cost	21,641		22,047
Gross Unrealized Gains	300		602
Gross Unrealized Losses	(87)		(51)
Net Unrealized Gains (losses)	213		551
Total fixed maturities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	432,621		445,669
Cost or Amortized Cost	427,658		440,559
Gross Unrealized Gains	6,524		6,392
Gross Unrealized Losses	(1,561)		(1,282)
Net Unrealized Gains (losses)	4,963		5,110
Available-for-sale securities continuous unrealized loss position [Abstract]
Number of Securities Less than 12 months	176		170
Number of Securities More than 12 months	52		58
Number of Securities, total	228		228
Available-for-sale securities continuous unrealized loss position, Fair Value [Abstract]
Fair value, 12 months or less	65,966		90,607
Fair value, 12 months or longer	24,190		19,283
Fair value, total	90,156		109,890
Available-for-sale securities continuous unrealized loss position, aggregate losses [Abstract]
Gross unrealized loss, less than 12 months	(792)		(483)
Gross unrealized loss, 12 months or longer	(769)		(799)
Gross unrealized loss, total	(1,561)		(1,282)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	1,419		550
Gross losses	(1,337)		(971)
Net realized gains (losses)	82		(421)
Financial institutions [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	13,205		12,394
Cost or Amortized Cost	5,618		5,925
Gross Unrealized Gains	7,627		6,542
Gross Unrealized Losses	(40)		(73)
Net Unrealized Gains (losses)	7,587		6,469
Industrial & Miscellaneous [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	102,172		95,188
Cost or Amortized Cost	58,786		52,202
Gross Unrealized Gains	44,261		44,568
Gross Unrealized Losses	(875)		(1,582)
Net Unrealized Gains (losses)	43,386		42,986
Total equity securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	115,377		107,582
Cost or Amortized Cost	64,404		58,127
Gross Unrealized Gains	51,888		51,110
Gross Unrealized Losses	(915)		(1,655)
Net Unrealized Gains (losses)	50,973		49,455
Available-for-sale securities continuous unrealized loss position [Abstract]
Number of Securities Less than 12 months	24		20
Number of Securities More than 12 months	2		11
Number of Securities, total	26		31
Available-for-sale securities continuous unrealized loss position, Fair Value [Abstract]
Fair value, 12 months or less	14,247		6,955
Fair value, 12 months or longer	244		6,640
Fair value, total	14,491		13,595
Available-for-sale securities continuous unrealized loss position, aggregate losses [Abstract]
Gross unrealized loss, less than 12 months	(896)		(842)
Gross unrealized loss, 12 months or longer	(19)		(813)
Gross unrealized loss, total	(915)		(1,655)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	11,712		524
Gross losses	(1,160)		(142)
Net realized gains (losses)	10,552		382
Total available-for-sale securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	547,998
Cost or Amortized Cost	492,062
Gross Unrealized Gains	58,412
Gross Unrealized Losses	(2,476)
Net Unrealized Gains (losses)	$ 55,936