Investments (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) Security Borrower	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Security Borrower	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Security
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Cost or amortized cost	$ 444,250		$ 444,250
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Applicable federal income taxes			(19,860)		$ (27,913)
Net unrealized gains - net of tax			$ 36,883		$ 51,840
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, total | Security	349		349		767
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, total	$ 158,462		$ 158,462		$ 218,647
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, total	(13,336)		(13,336)		(9,724)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
One year or less, Fair Value	74,675		74,675
Excess of one year to five years, Fair Value	244,552		244,552
Excess of five years to ten years, Fair Value	36,252		36,252
Excess of ten years, Fair Value	3,298		3,298
Contractual maturities, Fair Value	358,777		358,777
Asset-backed securities, Fair Value	83,842		83,842
Total, Fair Value	442,619		442,619
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
One year or less, Cost or Amortized Cost Basis	75,062		75,062
Excess of one year to five years, Cost or Amortized Cost Basis	245,370		245,370
Excess of five years to ten years, Cost or Amortized Cost Basis	36,889		36,889
Excess of ten years, Cost or Amortized Cost Basis	3,076		3,076
Contractual maturities, Cost or Amortized Cost Basis	360,397		360,397
Asset-backed securities, Cost or Amortized Cost Basis	83,853		83,853
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Limited partnerships - net gain (loss)	(6,301)	$ (1,064)	(2,061)	$ 7,204
Net realized gains (losses) on investments	(2,086)	658	491	12,817
Available for Sale Securities Gain Loss Activity [Abstract]
Realized net gains on the disposal of securities	7,957	2,223	7,544	5,837
Mark-to-market adjustment	(300)	(118)	(692)	151
Equity in gains (losses) of limited partnership investments - realized and unrealized	(6,301)	(1,064)	(2,061)	7,204
Write-downs based upon objective criteria	(4,396)	(441)	(5,503)	(546)
Recovery of prior write-downs upon sale or disposal	954	58	1,203	171
Net realized gains (losses) on investments	(2,086)	658	491	12,817
Net unrealized gains (losses) on investments	9,335		8,280
Net unrealized gains in limited partnership			4,967
Undistributed earnings of limited partnership, net of taxes	26,236		26,236
Committed funds for bridge loans	$ 17,000		$ 17,000
Number of separate borrowers related to bridge loan agreements | Borrower	2		2
U.S. Government Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	$ 110,095		$ 110,095		101,094
Cost or amortized cost	109,746		109,746		101,058
Gross unrealized gains	355		355		108
Gross unrealized losses	(6)		(6)		(72)
Net unrealized gains (losses)	349		349		36
Residential Mortgage-backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	5,116		5,116		6,066
Cost or amortized cost	4,886		4,886		5,830
Gross unrealized gains	244		244		273
Gross unrealized losses	(14)		(14)		(37)
Net unrealized gains (losses)	230		230		236
Commercial Mortgage-backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	29,601		29,601		36,440
Cost or amortized cost	29,735		29,735		36,210
Gross unrealized gains	374		374		630
Gross unrealized losses	(508)		(508)		(400)
Net unrealized gains (losses)	(134)		(134)		230
States and Municipal Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	114,304		114,304		113,777
Cost or amortized cost	113,700		113,700		113,133
Gross unrealized gains	946		946		784
Gross unrealized losses	(342)		(342)		(140)
Net unrealized gains (losses)	604		604		644
Corporate Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	162,294		162,294		166,966
Cost or amortized cost	163,733		163,733		170,822
Gross unrealized gains	2,350		2,350		2,005
Gross unrealized losses	(3,789)		(3,789)		(5,861)
Net unrealized gains (losses)	(1,439)		(1,439)		(3,856)
Foreign Government Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	21,209		21,209		27,466
Cost or amortized cost	22,450		22,450		28,332
Gross unrealized gains	286		286		114
Gross unrealized losses	(1,527)		(1,527)		(980)
Net unrealized gains (losses)	(1,241)		(1,241)		(866)
Total Fixed Maturities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	442,619		442,619		451,809
Cost or amortized cost	444,250		444,250		455,385
Gross unrealized gains	4,555		4,555		3,914
Gross unrealized losses	(6,186)		(6,186)		(7,490)
Net unrealized gains (losses)	$ (1,631)		$ (1,631)		$ (3,576)
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, 12 months or less | Security	209		209		591
Number of Securities, Greater than 12 months | Security	67		67		140
Number of Securities, total | Security	276		276		731
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 98,604		$ 98,604		$ 176,756
Fair value, Greater than 12 months	21,094		21,094		27,667
Fair value, total	119,698		119,698		204,423
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(4,939)		(4,939)		(6,083)
Gross unrealized loss, Greater than 12 months	(1,247)		(1,247)		(1,407)
Gross unrealized loss, total	(6,186)		(6,186)		(7,490)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	1,294	798	3,426	5,399
Gross losses	(5,087)	(1,259)	(8,876)	(3,411)
Net realized gains (losses)	(3,793)	(461)	(5,450)	1,988
Financial Institutions [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	20,161		20,161		25,343
Cost or amortized cost	9,356		9,356		10,100
Gross unrealized gains	10,826		10,826		15,303
Gross unrealized losses	(21)		(21)		(60)
Net unrealized gains (losses)	10,805		10,805		15,243
Industrial & Miscellaneous [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	122,353		122,353		136,764
Cost or amortized cost	74,784		74,784		68,678
Gross unrealized gains	54,698		54,698		70,260
Gross unrealized losses	(7,129)		(7,129)		(2,174)
Net unrealized gains (losses)	47,569		47,569		68,086
Total Equity Securities [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	142,514		142,514		162,107
Cost or amortized cost	84,140		84,140		78,778
Gross unrealized gains	65,524		65,524		85,563
Gross unrealized losses	(7,150)		(7,150)		(2,234)
Net unrealized gains (losses)	$ 58,374		$ 58,374		$ 83,329
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, 12 months or less | Security	61		61		33
Number of Securities, Greater than 12 months | Security	12		12		3
Number of Securities, total | Security	73		73		36
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 35,888		$ 35,888		$ 13,538
Fair value, Greater than 12 months	2,876		2,876		686
Fair value, total	38,764		38,764		14,224
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(6,181)		(6,181)		(2,170)
Gross unrealized loss, Greater than 12 months	(969)		(969)		(64)
Gross unrealized loss, total	(7,150)		(7,150)		(2,234)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	10,320	2,529	12,299	4,682
Gross losses	(2,312)	(346)	(4,297)	(1,057)
Net realized gains (losses)	8,008	$ 2,183	8,002	$ 3,625
Total Available-for-sale Securities [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Fair value	585,133		585,133		613,916
Cost or amortized cost	528,390		528,390		534,163
Gross unrealized gains	70,079		70,079		89,477
Gross unrealized losses	(13,336)		(13,336)		(9,724)
Net unrealized gains (losses)	$ 56,743		$ 56,743		$ 79,753