Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Schedule of Available-For-Sale Securities [Line Items]
Applicable federal income taxes			$ (18,565)		$ (14,319)
Net unrealized gains - net of tax			34,480		26,592
Number of other than temporarily impaired securities	6	3	6	3
Number of other than temporarily impaired securities loss recognized in accumulated other comprehensive income	3	1	3	1
Available-for-sale securities continuous unrealized loss position [Abstract]
Number of Securities, total	206		206		289
Available-for-sale securities continuous unrealized loss position, Fair Value [Abstract]
Fair value, total	91,868		91,868		106,933
Available-for-sale securities continuous unrealized loss position, aggregate losses [Abstract]
Gross unrealized loss, total	(2,971)		(2,971)		(4,538)
Available-for-sale securities debt maturities fair value [Abstract]
One year or less, Fair Value	160,953		160,953
Excess of one year to five years, Fair Value	203,862		203,862
Excess of five years to ten years, Fair Value	32,107		32,107
Excess of ten years, Fair Value	3,167		3,167
Total maturities, Fair Value	400,089		400,089
Asset-backed securities	43,495		43,495
Available-for-sale securities debt securities current	443,584		443,584
Available-for-sale securities debt maturities amortized cost basis [Abstract]
One year or less, Amortized Cost Basis	160,557		160,557
Excess of one year to five years, Amortized Cost Basis	201,413		201,413
Excess of five years to ten years, Amortized Cost Basis	31,611		31,611
Excess of ten years, Amortized Cost Basis	2,990		2,990
Total maturities, Amortized Cost Basis	396,571		396,571
Asset-backed securities	42,162		42,162
Available-for-sale securities debt maturities amortized cost basis, Total	438,733		438,733
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Limited partnerships - net gain (loss)	6,295	(16,061)	6,832	(21,238)
Totals	8,781	(17,460)	8,709	(20,892)
Available for sale securities gain loss activity [Abstract]
Realized net gains on the disposal of securities	1,659	1,312	1,454	3,356
Mark-to-market adjustment	456	(1,353)	144	(1,998)
Equity in gains (losses) of limited partnership investments - realized and unrealized	6,295	(16,061)	6,832	(21,238)
Write-downs based upon objective criteria	(411)	(1,376)	(756)	(1,494)
Recovery of prior write-downs upon sale or disposal	782	18	1,035	482
Totals	8,781	(17,460)	8,709	(20,892)
Net unrealized gain (loss) on investments	5,642		9,503
Unrealized losses in limited partnership			5,336
Undistributed earnings of limited partnership, net of taxes	19,786		19,786
U.S. government obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	70,686		70,686		73,137
Cost or Amortized Cost	70,640		70,640		73,009
Gross Unrealized Gains	70		70		139
Gross Unrealized Losses	(24)		(24)		(11)
Net Unrealized Gains (losses)	46		46		128
Government sponsored entities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value					349
Cost or Amortized Cost					345
Gross Unrealized Gains					4
Gross Unrealized Losses					0
Net Unrealized Gains (losses)					4
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	16,808		16,808		21,872
Cost or Amortized Cost	16,403		16,403		21,778
Gross Unrealized Gains	569		569		619
Gross Unrealized Losses	(164)		(164)		(525)
Net Unrealized Gains (losses)	405		405		94
Commercial mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	14,717		14,717		11,300
Cost or Amortized Cost	14,153		14,153		11,388
Gross Unrealized Gains	698		698		116
Gross Unrealized Losses	(134)		(134)		(204)
Net Unrealized Gains (losses)	564		564		(88)
States and municipal obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	195,300		195,300		190,035
Cost or Amortized Cost	194,211		194,211		188,991
Gross Unrealized Gains	1,142		1,142		1,275
Gross Unrealized Losses	(53)		(53)		(231)
Net Unrealized Gains (losses)	1,089		1,089		1,044
Corporate securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	124,240		124,240		91,646
Cost or Amortized Cost	121,860		121,860		91,949
Gross Unrealized Gains	3,455		3,455		1,429
Gross Unrealized Losses	(1,075)		(1,075)		(1,732)
Net Unrealized Gains (losses)	2,380		2,380		(303)
Foreign government obligations [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	21,833		21,833		21,121
Cost or Amortized Cost	21,466		21,466		21,483
Gross Unrealized Gains	460		460		168
Gross Unrealized Losses	(93)		(93)		(530)
Net Unrealized Gains (losses)	367		367		(362)
Total fixed maturities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	443,584		443,584		409,460
Cost or Amortized Cost	438,733		438,733		408,943
Gross Unrealized Gains	6,394		6,394		3,750
Gross Unrealized Losses	(1,543)		(1,543)		(3,233)
Net Unrealized Gains (losses)	4,851		4,851		517
Available-for-sale securities continuous unrealized loss position [Abstract]
Number of Securities Less than 12 months	129		129		206
Number of Securities More than 12 months	43		43		44
Number of Securities, total	172		172		250
Available-for-sale securities continuous unrealized loss position, Fair Value [Abstract]
Fair value, 12 months or less	70,996		70,996		86,470
Fair value, 12 months or longer	8,701		8,701		11,930
Fair value, total	79,697		79,697		98,400
Available-for-sale securities continuous unrealized loss position, aggregate losses [Abstract]
Gross unrealized loss, less than 12 months	(943)		(943)		(2,303)
Gross unrealized loss, 12 months or longer	(600)		(600)		(930)
Gross unrealized loss, total	(1,543)		(1,543)		(3,233)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	1,508	1,572	2,850	3,730
Gross losses	(801)	(2,048)	(2,952)	(3,917)
Net realized gains (losses)	707	(476)	(102)	(187)
Financial institutions [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	11,731		11,731		9,428
Cost or Amortized Cost	5,699		5,699		4,955
Gross Unrealized Gains	6,187		6,187		4,778
Gross Unrealized Losses	(155)		(155)		(305)
Net Unrealized Gains (losses)	6,032		6,032		4,473
Industrial & Miscellaneous [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	92,151		92,151		78,657
Cost or Amortized Cost	49,989		49,989		42,736
Gross Unrealized Gains	43,435		43,435		36,921
Gross Unrealized Losses	(1,273)		(1,273)		(1,000)
Net Unrealized Gains (losses)	42,162		42,162		35,921
Total equity securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	103,882		103,882		88,085
Cost or Amortized Cost	55,688		55,688		47,691
Gross Unrealized Gains	49,622		49,622		41,699
Gross Unrealized Losses	(1,428)		(1,428)		(1,305)
Net Unrealized Gains (losses)	48,194		48,194		40,394
Available-for-sale securities continuous unrealized loss position [Abstract]
Number of Securities Less than 12 months	11		11		35
Number of Securities More than 12 months	23		23		4
Number of Securities, total	34		34		39
Available-for-sale securities continuous unrealized loss position, Fair Value [Abstract]
Fair value, 12 months or less	4,686		4,686		8,317
Fair value, 12 months or longer	7,485		7,485		216
Fair value, total	12,171		12,171		8,533
Available-for-sale securities continuous unrealized loss position, aggregate losses [Abstract]
Gross unrealized loss, less than 12 months	(365)		(365)		(1,275)
Gross unrealized loss, 12 months or longer	(1,063)		(1,063)		(30)
Gross unrealized loss, total	(1,428)		(1,428)		(1,305)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	2,132	272	2,807	2,501
Gross losses	(353)	(1,195)	(828)	(1,968)
Net realized gains (losses)	1,779	(923)	1,979	533
Total Available-for-Sale Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	547,466		547,466		497,545
Cost or Amortized Cost	494,421		494,421		456,634
Gross Unrealized Gains	56,016		56,016		45,449
Gross Unrealized Losses	(2,971)		(2,971)		(4,538)
Net Unrealized Gains (losses)	$ 53,045		$ 53,045		$ 40,911