Investments (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) Security	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) Security Partnership	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Security
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	$ 486,137		$ 486,137
Cost or amortized cost	$ 484,981		484,981
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Applicable federal income taxes			(20,144)		$ (20,959)
Net unrealized gains - net of tax			$ 37,410		$ 38,924
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, total | Security	363		363		569
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, total	$ 249,141		$ 249,141		$ 340,035
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, total	(7,105)		(7,105)		(14,644)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
One year or less, Fair Value	92,876		92,876
Excess of one year to five years, Fair Value	261,413		261,413
Excess of five years to ten years, Fair Value	43,440		43,440
Excess of ten years, Fair Value	3,907		3,907
Contractual maturities, Fair Value	401,636		401,636
Asset-backed securities, Fair Value	84,501		84,501
Total, Fair Value	486,137		486,137
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
One year or less, Cost or Amortized Cost Basis	92,984		92,984
Excess of one year to five years, Cost or Amortized Cost Basis	261,261		261,261
Excess of five years to ten years, Cost or Amortized Cost Basis	42,700		42,700
Excess of ten years, Cost or Amortized Cost Basis	3,595		3,595
Contractual maturities, Cost or Amortized Cost Basis	400,540		400,540
Asset-backed securities, Cost or Amortized Cost Basis	84,441		84,441
Cost or amortized cost	484,981		484,981
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Limited partnerships - net gain (loss)	4,403	$ (6,301)	3,201	$ (2,061)
Net realized gains (losses) on investments	7,732	(2,086)	17,024	491
Available for Sale Securities Gain Loss Activity [Abstract]
Realized net gains on the disposal of securities	3,482	7,957	10,649	7,544
Mark-to-market adjustment	108	(300)	(326)	(692)
Equity in gains (losses) of limited partnership investments - realized and unrealized	4,403	(6,301)	3,201	(2,061)
Write-downs based upon objective criteria	(1,844)	(4,396)	(4,999)	(5,503)
Recovery of prior write-downs upon sale or disposal	1,583	954	8,499	1,203
Net realized gains (losses) on investments	7,732	(2,086)	17,024	491
Undistributed earnings of limited partnership, net of taxes	28,606		28,606
Committed funds for bridge loans	0		0
Total investment in limited partnerships	46,855		$ 46,855
Number of partnerships investment | Partnership			2
Investment assets other than limited partnership			$ 39,572
U.S. Government Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	96,573		96,573		103,245
Cost or amortized cost	96,209		96,209		103,448
Gross unrealized gains	366		366		56
Gross unrealized losses	(2)		(2)		(259)
Net unrealized gains (losses)	364		364		(203)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	96,573		96,573		103,245
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	96,209		96,209		103,448
Residential Mortgage-backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	5,608		5,608		4,776
Cost or amortized cost	5,433		5,433		4,668
Gross unrealized gains	221		221		162
Gross unrealized losses	(46)		(46)		(54)
Net unrealized gains (losses)	175		175		108
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	5,608		5,608		4,776
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	5,433		5,433		4,668
Commercial Mortgage-backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	29,809		29,809		30,595
Cost or amortized cost	29,651		29,651		30,977
Gross unrealized gains	952		952		247
Gross unrealized losses	(794)		(794)		(629)
Net unrealized gains (losses)	158		158		(382)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	29,809		29,809		30,595
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	29,651		29,651		30,977
States and Municipal Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	131,697		131,697		110,578
Cost or amortized cost	130,783		130,783		109,932
Gross unrealized gains	1,144		1,144		806
Gross unrealized losses	(230)		(230)		(160)
Net unrealized gains (losses)	914		914		646
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	131,697		131,697		110,578
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	130,783		130,783		109,932
Corporate Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	197,677		197,677		164,025
Cost or amortized cost	196,984		196,984		168,137
Gross unrealized gains	3,248		3,248		2,445
Gross unrealized losses	(2,555)		(2,555)		(6,557)
Net unrealized gains (losses)	693		693		(4,112)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	197,677		197,677		164,025
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	196,984		196,984		168,137
Foreign Government Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	24,773		24,773		23,965
Cost or amortized cost	25,921		25,921		25,416
Gross unrealized gains	363		363		404
Gross unrealized losses	(1,511)		(1,511)		(1,855)
Net unrealized gains (losses)	(1,148)		(1,148)		(1,451)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	24,773		24,773		23,965
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	25,921		25,921		25,416
Total Fixed Maturities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	486,137		486,137		437,184
Cost or amortized cost	484,981		484,981		442,578
Gross unrealized gains	6,294		6,294		4,120
Gross unrealized losses	(5,138)		(5,138)		(9,514)
Net unrealized gains (losses)	$ 1,156		$ 1,156		$ (5,394)
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, 12 months or less | Security	251		251		328
Number of Securities, Greater than 12 months | Security	54		54		168
Number of Securities, total | Security	305		305		496
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 198,916		$ 198,916		$ 205,475
Fair value, Greater than 12 months	19,596		19,596		108,043
Fair value, total	218,512		218,512		313,518
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(2,882)		(2,882)		(5,070)
Gross unrealized loss, Greater than 12 months	(2,256)		(2,256)		(4,444)
Gross unrealized loss, total	(5,138)		(5,138)		(9,514)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	486,137		486,137		437,184
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	484,981		484,981		442,578
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	7,496	1,294	9,338	3,426
Gross losses	(8,434)	(5,087)	(12,470)	(8,876)
Net realized gains (losses)	(938)	(3,793)	(3,132)	(5,450)
Financial Institutions [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	20,251		20,251		21,694
Cost or amortized cost	13,261		13,261		10,836
Gross unrealized gains	7,299		7,299		11,069
Gross unrealized losses	(309)		(309)		(211)
Net unrealized gains (losses)	6,990		6,990		10,858
Industrial & Miscellaneous [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	114,203		114,203		123,804
Cost or amortized cost	64,795		64,795		69,385
Gross unrealized gains	51,066		51,066		59,338
Gross unrealized losses	(1,658)		(1,658)		(4,919)
Net unrealized gains (losses)	49,408		49,408		54,419
Total Equity Securities [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	134,454		134,454		145,498
Cost or amortized cost	78,056		78,056		80,221
Gross unrealized gains	58,365		58,365		70,407
Gross unrealized losses	(1,967)		(1,967)		(5,130)
Net unrealized gains (losses)	$ 56,398		$ 56,398		$ 65,277
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, 12 months or less | Security	58		58		73
Number of Securities, Greater than 12 months | Security	0		0		0
Number of Securities, total | Security	58		58		73
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 30,629		$ 30,629		$ 26,517
Fair value, Greater than 12 months	0		0		0
Fair value, total	30,629		30,629		26,517
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(1,967)		(1,967)		(5,130)
Gross unrealized loss, Greater than 12 months	0		0		0
Gross unrealized loss, total	(1,967)		(1,967)		(5,130)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	5,086	10,320	21,722	12,299
Gross losses	(819)	(2,312)	(4,767)	(4,297)
Net realized gains (losses)	4,267	$ 8,008	16,955	$ 8,002
Total Available-for-sale Securities [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Fair value	620,591		620,591		582,682
Cost or amortized cost	563,037		563,037		522,799
Gross unrealized gains	64,659		64,659		74,527
Gross unrealized losses	(7,105)		(7,105)		(14,644)
Net unrealized gains (losses)	$ 57,554		$ 57,554		$ 59,883