Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013 securities		Dec. 31, 2012 securities
Schedule of Available-for-sale Securities [Line Items]
Decommissioning Fund Investments	$ 202,907		$ 187,053
Marketable Securities Fair Value Less than 12 Months	32,204	[1]	17,786	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(1,255)	[1]	(543)	[2]
Marketable Securities Fair Value 12 Months or Longer	13,748	[1]	10,633	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(745)	[1]	(364)	[2]
Marketable Securities Fair Value Total	45,952	[1]	28,419	[2]
Marketable Securities Unrealized Losses Total	(2,000)	[1]	(907)	[2]
Number of investable securities	112		65
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	31,197	[1]	14,183	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(1,159)	[1]	(134)	[2]
Marketable Securities Fair Value 12 Months or Longer	13,531	[1]	10,633	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(727)	[1]	(364)	[2]
Marketable Securities Fair Value Total	44,728	[1]	24,816	[2]
Marketable Securities Unrealized Losses Total	(1,886)	[1]	(498)	[2]
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	1,909	[1]	1,792	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(100)	[1]	(5)	[2]
Marketable Securities Fair Value 12 Months or Longer	729	[1]	416	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(50)	[1]	(9)	[2]
Marketable Securities Fair Value Total	2,638	[1]	2,208	[2]
Marketable Securities Unrealized Losses Total	(150)	[1]	(14)	[2]
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	10,664	[1]	6,633	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(477)	[1]	(79)	[2]
Marketable Securities Fair Value 12 Months or Longer	7,086	[1]	4,457	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(344)	[1]	(114)	[2]
Marketable Securities Fair Value Total	17,750	[1]	11,090	[2]
Marketable Securities Unrealized Losses Total	(821)	[1]	(193)	[2]
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	15,360	[1]	5,306	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(455)	[1]	(39)	[2]
Marketable Securities Fair Value 12 Months or Longer	5,316	[1]	5,760	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(328)	[1]	(241)	[2]
Marketable Securities Fair Value Total	20,676	[1]	11,066	[2]
Marketable Securities Unrealized Losses Total	(783)	[1]	(280)	[2]
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	3,264	[1]	452	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(127)	[1]	(11)	[2]
Marketable Securities Fair Value 12 Months or Longer	400	[1]	0	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(5)	[1]	0	[2]
Marketable Securities Fair Value Total	3,664	[1]	452	[2]
Marketable Securities Unrealized Losses Total	(132)	[1]	(11)	[2]
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	1,007	[1]	3,603	[2]
Marketable Securities Unrealized Losses Less Than 12 Months	(96)	[1]	(409)	[2]
Marketable Securities Fair Value 12 Months or Longer	217	[1]	0	[2]
Marketable Securities Unrealized Losses 12 Months or Longer	(18)	[1]	0	[2]
Marketable Securities Fair Value Total	1,224	[1]	3,603	[2]
Marketable Securities Unrealized Losses Total	$ (114)	[1]	$ (409)	[2]

[1] Includes approximately 112 securities.

[2] Includes approximately 65 securities.