Investments (Summary of Gross Unrealized Losses for Investments that have been Continuously in Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Fair Value 12 months or less	$ 207,117	$ 200,483
Unrealized Losses 12 months or less	(1,696)	(2,760)
Fair Value Longer than 12 months	13,001	26,355
Unrealized Losses Longer than 12 months	(365)	(2,109)
Total Fair Value	220,118	226,838
Total Unrealized Losses	(2,061)	(4,869)
Other Investments [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	614
Total Fair Value	614
Equity Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	5,653	4,109
Unrealized Losses 12 months or less	(598)	(483)
Fair Value Longer than 12 months	2,106	2,037
Unrealized Losses Longer than 12 months	(43)	(307)
Total Fair Value	7,759	6,146
Total Unrealized Losses	(641)	(790)
Debt Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	200,850	196,374
Unrealized Losses 12 months or less	(1,098)	(2,277)
Fair Value Longer than 12 months	10,895	24,318
Unrealized Losses Longer than 12 months	(322)	(1,802)
Total Fair Value	211,745	220,692
Total Unrealized Losses	(1,420)	(4,079)
Us Treasury Securities and Obligations of U.S. Government [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	36,947	7,037
Unrealized Losses 12 months or less	(14)	(20)
Total Fair Value	36,947	7,037
Total Unrealized Losses	(14)	(20)
Corporate Bonds [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	72,355	86,592
Unrealized Losses 12 months or less	(161)	(575)
Total Fair Value	72,355	86,592
Total Unrealized Losses	(161)	(575)
Collateralized Corporate Bank Loans [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	36,049	2,637
Unrealized Losses 12 months or less	(150)	(7)
Fair Value Longer than 12 months	2,408	8,314
Unrealized Losses Longer than 12 months	(142)	(163)
Total Fair Value	38,457	10,951
Total Unrealized Losses	(292)	(170)
Municipal Bonds [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	42,718	70,633
Unrealized Losses 12 months or less	(524)	(1,327)
Fair Value Longer than 12 months	6,859	13,574
Unrealized Losses Longer than 12 months	(177)	(1,634)
Total Fair Value	49,577	84,207
Total Unrealized Losses	(701)	(2,961)
Mortgage Backed [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Fair Value 12 months or less	12,781	29,475
Unrealized Losses 12 months or less	(249)	(348)
Fair Value Longer than 12 months	1,628	2,430
Unrealized Losses Longer than 12 months	(3)	(5)
Total Fair Value	14,409	31,905
Total Unrealized Losses	$ (252)	$ (353)