Investments (Investment Gains and Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 1,274,085	$ 1,223,747
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	69,779	18,604
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,525	11,312
Debt Securities, Available-for-sale	1,341,339	1,231,039
Debt Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,525	11,312
US Treasury Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	9,749	9,864
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,733	1,410
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-sale	11,482	11,274
US Government Agencies Debt Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,528	3,540
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,015	740
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-sale	4,543	4,280
US States and Political Subdivisions Debt Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	651,598	713,991
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	25,193	7,614
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	351	1,490
Debt Securities, Available-for-sale	676,440	720,115
Corporate Debt Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	481,406	384,817
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	30,533	6,725
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,171	9,746
Debt Securities, Available-for-sale	509,768	381,796
Commercial Mortgage Backed Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,109	39,694
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2	386
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	66
Debt Securities, Available-for-sale	1,111	40,014
Residential Mortgage Backed Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	116,364	66,960
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	11,280	1,726
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2	2
Debt Securities, Available-for-sale	127,642	68,684
Asset-backed Securities [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	10,229	4,764
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	8
Debt Securities, Available-for-sale	10,233	4,757
Foreign Government, Non-US [Member]
Gross Unrealized Gains and Losses [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	102	117
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	18	2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-sale	$ 120	$ 119