Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2017 USD ($) securities		Dec. 31, 2016 USD ($) securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		$ 65,763	[1]	$ 86,509	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(1,095)	[1]	(1,844)	[2]
Marketable Securities Fair Value 12 Months or Longer		19,103	[1]	24,571	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(1,366)	[1]	(1,401)	[2]
Marketable Securities Fair Value Total		84,866	[1]	111,080	[2]
Marketable Securities Unrealized Losses Total		$ (2,461)	[1]	$ (3,245)	[2]
Number of securities | securities		136		152
Debt Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		$ 65,045	[1]	$ 60,804	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(1,030)	[1]	(1,567)	[2]
Marketable Securities Fair Value 12 Months or Longer		19,103	[1]	24,571	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(1,366)	[1]	(1,401)	[2]
Marketable Securities Fair Value Total		84,148	[1]	85,375	[2]
Marketable Securities Unrealized Losses Total		(2,396)	[1]	(2,968)	[2]
Federal Agency Mortgage Backed Securities
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		15,446	[1]	11,582	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(188)	[1]	(239)	[2]
Marketable Securities Fair Value 12 Months or Longer		415	[1]	436	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(19)	[1]	(22)	[2]
Marketable Securities Fair Value Total		15,861	[1]	12,018	[2]
Marketable Securities Unrealized Losses Total		(207)	[1]	(261)	[2]
U.S. Government Bonds
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		35,388	[1]	31,655	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(598)	[1]	(762)	[2]
Marketable Securities Fair Value 12 Months or Longer		9,816	[1]	17,976	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(630)	[1]	(835)	[2]
Marketable Securities Fair Value Total		45,204	[1]	49,631	[2]
Marketable Securities Unrealized Losses Total		(1,228)	[1]	(1,597)	[2]
Municipal Obligations
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		6,903	[1]	9,596	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(165)	[1]	(394)	[2]
Marketable Securities Fair Value 12 Months or Longer		5,928	[1]	4,067	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(482)	[1]	(372)	[2]
Marketable Securities Fair Value Total		12,831	[1]	13,663	[2]
Marketable Securities Unrealized Losses Total		(647)	[1]	(766)	[2]
Corporate Obligations
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		7,308	[1]	7,971	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(79)	[1]	(172)	[2]
Marketable Securities Fair Value 12 Months or Longer		2,944	[1]	2,092	[2]
Marketable Securities Unrealized Losses 12 Months or Longer		(235)	[1]	(172)	[2]
Marketable Securities Fair Value Total		10,252	[1]	10,063	[2]
Marketable Securities Unrealized Losses Total		(314)	[1]	(344)	[2]
Common Stock
Financial Instruments and Investments [Line Items]
Marketable Securities Fair Value Less than 12 Months		718	[1]	2,760	[2]
Marketable Securities Unrealized Losses Less Than 12 Months		(65)	[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		718	[1]	2,760	[2]
Marketable Securities Unrealized Losses Total		$ (65)	[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 136 securities.

[2] Includes 152 securities.