Investments (Schedule of aggregate fair value and unrealized loss) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Less than 12 months Fair Value	$ 171,185	$ 103,806
Less than 12 months Unrealized Losses	(4,504)	(1,143)
Greater than 12 months Fair Value	16,023	15,430
Greater than 12 months Unrealized Losses	(722)	(468)
Fair Value, Total	187,208	119,236
Unrealized Losses, Total	(5,226)	(1,611)
Fixed income securities [Member]
Less than 12 months Fair Value	163,183	99,297
Less than 12 months Unrealized Losses	(3,292)	(690)
Greater than 12 months Fair Value	15,201	14,957
Greater than 12 months Unrealized Losses	(606)	(268)
Fair Value, Total	178,384	114,254
Unrealized Losses, Total	(3,898)	(958)
Fixed income securities [Member] | U.S. Government and agencies [Member]
Less than 12 months Fair Value	9,919	6,442
Less than 12 months Unrealized Losses	(208)	(54)
Greater than 12 months Fair Value	748	497
Greater than 12 months Unrealized Losses	(3)	(3)
Fair Value, Total	10,667	6,939
Unrealized Losses, Total	(211)	(57)
Fixed income securities [Member] | Obligations of states and political subdivisions [Member]
Less than 12 months Fair Value	28,068	28,219
Less than 12 months Unrealized Losses	(548)	(251)
Greater than 12 months Fair Value	3,959	3,593
Greater than 12 months Unrealized Losses	(173)	(66)
Fair Value, Total	32,027	31,812
Unrealized Losses, Total	(721)	(317)
Fixed income securities [Member] | Corporate securities [Member]
Less than 12 months Fair Value	67,967	39,025
Less than 12 months Unrealized Losses	(1,560)	(201)
Greater than 12 months Fair Value	1,122	1,195
Greater than 12 months Unrealized Losses	(40)	(19)
Fair Value, Total	69,089	40,220
Unrealized Losses, Total	(1,600)	(220)
Fixed income securities [Member] | Residential mortgage-backed securities [Member]
Less than 12 months Fair Value	28,800	7,573
Less than 12 months Unrealized Losses	(558)	(40)
Greater than 12 months Fair Value	6,542	7,248
Greater than 12 months Unrealized Losses	(286)	(117)
Fair Value, Total	35,342	14,821
Unrealized Losses, Total	(844)	(157)
Fixed income securities [Member] | Commercial mortgage-backed securities [Member]
Less than 12 months Fair Value	12,976	4,652
Less than 12 months Unrealized Losses	(233)	(64)
Greater than 12 months Fair Value	1,606	1,643
Greater than 12 months Unrealized Losses	(91)	(55)
Fair Value, Total	14,582	6,295
Unrealized Losses, Total	(324)	(119)
Fixed income securities [Member] | Asset backed securities [Member]
Less than 12 months Fair Value	15,453	13,386
Less than 12 months Unrealized Losses	(185)	(80)
Greater than 12 months Fair Value	1,224	781
Greater than 12 months Unrealized Losses	(13)	(8)
Fair Value, Total	16,677	14,167
Unrealized Losses, Total	(198)	(88)
Equity Securities [Member]
Less than 12 months Fair Value	8,002	4,509
Less than 12 months Unrealized Losses	(1,212)	(453)
Greater than 12 months Fair Value	822	473
Greater than 12 months Unrealized Losses	(116)	(200)
Fair Value, Total	8,824	4,982
Unrealized Losses, Total	(1,328)	(653)
Equity Securities [Member] | Basic materials [Member]
Less than 12 months Fair Value	415
Less than 12 months Unrealized Losses	(14)
Greater than 12 months Fair Value
Greater than 12 months Unrealized Losses
Fair Value, Total	415
Unrealized Losses, Total	(14)
Equity Securities [Member] | Communications [Member]
Less than 12 months Fair Value	430	840
Less than 12 months Unrealized Losses	(79)	(48)
Greater than 12 months Fair Value	630	107
Greater than 12 months Unrealized Losses	(65)	(106)
Fair Value, Total	1,060	947
Unrealized Losses, Total	(144)	(154)
Equity Securities [Member] | Consumer, cyclical [Member]
Less than 12 months Fair Value	376	898
Less than 12 months Unrealized Losses	(62)	(116)
Greater than 12 months Fair Value		214
Greater than 12 months Unrealized Losses		(4)
Fair Value, Total	376	1,112
Unrealized Losses, Total	(62)	(120)
Equity Securities [Member] | Consumer, non-cyclical [Member]
Less than 12 months Fair Value	3,036	1,894
Less than 12 months Unrealized Losses	(425)	(125)
Greater than 12 months Fair Value
Greater than 12 months Unrealized Losses
Fair Value, Total	3,036	1,894
Unrealized Losses, Total	(425)	(125)
Equity Securities [Member] | Energy [Member]
Less than 12 months Fair Value	132	243
Less than 12 months Unrealized Losses	(319)	(44)
Greater than 12 months Fair Value
Greater than 12 months Unrealized Losses
Fair Value, Total	132	243
Unrealized Losses, Total	(319)	(44)
Equity Securities [Member] | Financial [Member]
Less than 12 months Fair Value	1,626
Less than 12 months Unrealized Losses	(120)
Greater than 12 months Fair Value
Greater than 12 months Unrealized Losses
Fair Value, Total	1,626
Unrealized Losses, Total	(120)
Equity Securities [Member] | Industrial [Member]
Less than 12 months Fair Value	1,555
Less than 12 months Unrealized Losses	(118)
Greater than 12 months Fair Value
Greater than 12 months Unrealized Losses
Fair Value, Total	1,555
Unrealized Losses, Total	(118)
Equity Securities [Member] | Technology [Member]
Less than 12 months Fair Value	432	634
Less than 12 months Unrealized Losses	(75)	(120)
Greater than 12 months Fair Value	192	152
Greater than 12 months Unrealized Losses	(51)	(90)
Fair Value, Total	624	786
Unrealized Losses, Total	$ (126)	$ (210)