Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2017 USD ($) securities		Dec. 31, 2016 USD ($) securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		$ 63,121	[1]	$ 86,509	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(1,470)	[1]	(1,844)	[2]
Marketable Securities Fair Value 12 Months or Longer		17,204	[1]	24,571	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(1,186)	[1]	(1,401)	[2]
Marketable Securities Fair Value Total		80,325	[1]	111,080	[2]
Marketable Securities Unrealized Losses Total		$ (2,656)	[1]	$ (3,245)	[2]
Number of securities | securities		139		152
Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		$ 62,580	[1]	$ 60,804	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(1,417)	[1]	(1,567)	[2]
Marketable Securities Fair Value 12 Months or Longer		17,204	[1]	24,571	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(1,186)	[1]	(1,401)	[2]
Marketable Securities Fair Value Total		79,784	[1]	85,375	[2]
Marketable Securities Unrealized Losses Total		(2,603)	[1]	(2,968)	[2]
Federal Agency Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		11,142	[1]	11,582	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(249)	[1]	(239)	[2]
Marketable Securities Fair Value 12 Months or Longer		424	[1]	436	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(23)	[1]	(22)	[2]
Marketable Securities Fair Value Total		11,566	[1]	12,018	[2]
Marketable Securities Unrealized Losses Total		(272)	[1]	(261)	[2]
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		32,621	[1]	31,655	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(739)	[1]	(762)	[2]
Marketable Securities Fair Value 12 Months or Longer		9,876	[1]	17,976	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(570)	[1]	(835)	[2]
Marketable Securities Fair Value Total		42,497	[1]	49,631	[2]
Marketable Securities Unrealized Losses Total		(1,309)	[1]	(1,597)	[2]
Municipal Obligations
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		9,152	[1]	9,596	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(298)	[1]	(394)	[2]
Marketable Securities Fair Value 12 Months or Longer		4,413	[1]	4,067	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(385)	[1]	(372)	[2]
Marketable Securities Fair Value Total		13,565	[1]	13,663	[2]
Marketable Securities Unrealized Losses Total		(683)	[1]	(766)	[2]
Corporate Obligations
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		9,665	[1]	7,971	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(131)	[1]	(172)	[2]
Marketable Securities Fair Value 12 Months or Longer		2,491	[1]	2,092	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(208)	[1]	(172)	[2]
Marketable Securities Fair Value Total		12,156	[1]	10,063	[2]
Marketable Securities Unrealized Losses Total		(339)	[1]	(344)	[2]
Common Stock
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		541	[1]	2,760	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(53)	[1]	(167)	[2]
Marketable Securities Fair Value 12 Months or Longer		0	[1]	0	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		0	[1]	0	[2]
Marketable Securities Fair Value Total		541	[1]	2,760	[2]
Marketable Securities Unrealized Losses Total		$ (53)	[1]	(167)	[2]
Institutional Funds-International Equity
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months	[2]			22,945
Marketable Securities Unrealized Losses Less Than 12 Months	[2]			(110)
Marketable Securities Fair Value 12 Months or Longer	[2]			0
Marketable Securities Unrealized Losses 12 Months or Longer	[2]			0
Marketable Securities Fair Value Total	[2]			22,945
Marketable Securities Unrealized Losses Total	[2]			$ (110)

[1] Includes 139 securities.

[2] Includes 152 securities.