Investments (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) Security Borrower Partnership	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) Security
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	$ 470,983
Cost or amortized cost	474,545
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Applicable federal income taxes	(16,625)		$ (20,959)
Net unrealized gains - net of tax	$ 30,874		$ 38,924
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, total | Security	409		569
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, total	$ 210,802		$ 340,035
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, total	(13,284)		(14,644)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
One year or less, Fair Value	148,336
Excess of one year to five years, Fair Value	201,404
Excess of five years to ten years, Fair Value	38,182
Excess of ten years, Fair Value	1,749
Contractual maturities, Fair Value	389,671
Asset-backed securities, Fair Value	81,312
Total, Fair Value	470,983
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
One year or less, Cost or Amortized Cost Basis	148,846
Excess of one year to five years, Cost or Amortized Cost Basis	201,288
Excess of five years to ten years, Cost or Amortized Cost Basis	38,489
Excess of ten years, Cost or Amortized Cost Basis	1,943
Contractual maturities, Cost or Amortized Cost Basis	390,566
Asset-backed securities, Cost or Amortized Cost Basis	83,979
Cost or amortized cost	474,545
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Limited partnerships - net gain (loss)	(2,179)	$ 4,533
Net realized gains on investments	9,012	3,743
Available for Sale Securities Gain Loss Activity [Abstract]
Realized net gains (losses) on the disposal of securities	8,309	(288)
Mark-to-market adjustment	(301)	(288)
Equity in gains (losses) of limited partnership investments - realized and unrealized	(2,179)	4,533
Write-downs based upon objective criteria	(2,060)	(214)
Recovery of prior write-downs upon sale or disposal	5,243	0
Net realized gains on investments	9,012	3,743
Net unrealized gains on investments	874
Net unrealized gains in limited partnership	5,934
Undistributed earnings of limited partnership, net of taxes	25,186
Committed funds for bridge loans	$ 5,000
Number of separate borrowers related to bridge loan agreements | Borrower	1
Total investment in limited partnerships	$ 43,800
Number of partnerships investment | Partnership	2
Investment assets other than limited partnership	$ 134,000
U.S. Government Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	128,428		103,245
Cost or amortized cost	128,128		103,448
Gross unrealized gains	313		56
Gross unrealized losses	(13)		(259)
Net unrealized gains (losses)	300		(203)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	128,428		103,245
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	128,128		103,448
Residential Mortgage-backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	4,534		4,776
Cost or amortized cost	4,477		4,668
Gross unrealized gains	133		162
Gross unrealized losses	(76)		(54)
Net unrealized gains (losses)	57		108
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	4,534		4,776
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	4,477		4,668
Commercial Mortgage-backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	32,374		30,595
Cost or amortized cost	32,585		30,977
Gross unrealized gains	605		247
Gross unrealized losses	(816)		(629)
Net unrealized gains (losses)	(211)		(382)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	32,374		30,595
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	32,585		30,977
States and Municipal Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	111,882		110,578
Cost or amortized cost	110,796		109,932
Gross unrealized gains	1,214		806
Gross unrealized losses	(128)		(160)
Net unrealized gains (losses)	1,086		646
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	111,882		110,578
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	110,796		109,932
Corporate Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	168,393		164,025
Cost or amortized cost	172,043		168,137
Gross unrealized gains	3,159		2,445
Gross unrealized losses	(6,809)		(6,557)
Net unrealized gains (losses)	(3,650)		(4,112)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	168,393		164,025
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	172,043		168,137
Foreign Government Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	25,372		23,965
Cost or amortized cost	26,516		25,416
Gross unrealized gains	470		404
Gross unrealized losses	(1,614)		(1,855)
Net unrealized gains (losses)	(1,144)		(1,451)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	25,372		23,965
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	26,516		25,416
Total Fixed Maturities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Fair value	470,983		437,184
Cost or amortized cost	474,545		442,578
Gross unrealized gains	5,894		4,120
Gross unrealized losses	(9,456)		(9,514)
Net unrealized gains (losses)	$ (3,562)		$ (5,394)
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, 12 months or less | Security	297		328
Number of Securities, Greater than 12 months | Security	51		168
Number of Securities, total | Security	348		496
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 158,578		$ 205,475
Fair value, Greater than 12 months	16,419		108,043
Fair value, total	174,997		313,518
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(7,200)		(5,070)
Gross unrealized loss, Greater than 12 months	(2,256)		(4,444)
Gross unrealized loss, total	(9,456)		(9,514)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
Total, Fair Value	470,983		437,184
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
Cost or amortized cost	474,545		442,578
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	1,277	1,147
Gross losses	(2,896)	(1,933)
Net realized gains (losses)	(1,619)	(786)
Financial Institutions [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	23,150		21,694
Cost or amortized cost	13,572		10,836
Gross unrealized gains	10,011		11,069
Gross unrealized losses	(433)		(211)
Net unrealized gains (losses)	9,578		10,858
Industrial & Miscellaneous [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	114,893		123,804
Cost or amortized cost	73,410		69,385
Gross unrealized gains	44,878		59,338
Gross unrealized losses	(3,395)		(4,919)
Net unrealized gains (losses)	41,483		54,419
Total Equity Securities [Member]
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Fair value	138,043		145,498
Cost or amortized cost	86,982		80,221
Gross unrealized gains	54,889		70,407
Gross unrealized losses	(3,828)		(5,130)
Net unrealized gains (losses)	$ 51,061		$ 65,277
Available-for-sale Securities Continuous Unrealized Loss Position [Abstract]
Number of Securities, 12 months or less | Security	61		73
Number of Securities, Greater than 12 months | Security	0		0
Number of Securities, total | Security	61		73
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 35,805		$ 26,517
Fair value, Greater than 12 months	0		0
Fair value, total	35,805		26,517
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(3,828)		(5,130)
Gross unrealized loss, Greater than 12 months	0		0
Gross unrealized loss, total	(3,828)		(5,130)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	15,510	749
Gross losses	(2,700)	(753)
Net realized gains (losses)	12,810	$ (4)
Total Available-for-sale Securities [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Fair value	609,026		582,682
Cost or amortized cost	561,527		522,799
Gross unrealized gains	60,783		74,527
Gross unrealized losses	(13,284)		(14,644)
Net unrealized gains (losses)	$ 47,499		$ 59,883