Investments (Summary of Gross Unrealized Loss Position) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	$ 200,483	$ 291,131
Unrealized Losses 12 months or less	(2,760)	(5,269)
Fair Value Longer than 12 months	26,355	28,890
Unrealized Losses Longer than 12 months	(2,109)	(5,604)
Fair Value Total	226,838	320,021
Unrealized Losses Total	(4,869)	(10,873)
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less
Unrealized Losses 12 months or less
Fair Value Longer than 12 months
Unrealized Losses Longer than 12 months
Fair Value Total
Unrealized Losses Total
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	196,374	284,547
Unrealized Losses 12 months or less	(2,277)	(4,431)
Fair Value Longer than 12 months	24,318	28,890
Unrealized Losses Longer than 12 months	(1,802)	(5,604)
Fair Value Total	220,692	313,437
Unrealized Losses Total	(4,079)	(10,035)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	4,109	6,584
Unrealized Losses 12 months or less	(483)	(838)
Fair Value Longer than 12 months	2,037
Unrealized Losses Longer than 12 months	(307)
Fair Value Total	6,146	6,584
Unrealized Losses Total	(790)	(838)
U.S. Treasury securities and obligations of U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	7,037	41,428
Unrealized Losses 12 months or less	(20)	(61)
Fair Value Total	7,037	41,428
Unrealized Losses Total	(20)	(61)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	86,592	96,475
Unrealized Losses 12 months or less	(575)	(1,822)
Fair Value Total	86,592	96,475
Unrealized Losses Total	(575)	(1,822)
Collateralized Corporate Bank Loans [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	2,637	65,868
Unrealized Losses 12 months or less	(7)	(1,758)
Fair Value Longer than 12 months	8,314	3,532
Unrealized Losses Longer than 12 months	(163)	(124)
Fair Value Total	10,951	69,400
Unrealized Losses Total	(170)	(1,882)
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	70,633	44,525
Unrealized Losses 12 months or less	(1,327)	(488)
Fair Value Longer than 12 months	13,574	25,310
Unrealized Losses Longer than 12 months	(1,634)	(5,478)
Fair Value Total	84,207	69,835
Unrealized Losses Total	(2,961)	(5,966)
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	29,475	36,251
Unrealized Losses 12 months or less	(348)	(302)
Fair Value Longer than 12 months	2,430	48
Unrealized Losses Longer than 12 months	(5)	(2)
Fair Value Total	31,905	36,299
Unrealized Losses Total	$ (353)	$ (304)