Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013 securities		Dec. 31, 2012 securities
Schedule of Available-for-sale Securities [Line Items]
Decommissioning Fund Investments	$ 196,166		$ 187,053
Marketable Securities Fair Value Less than 12 Months	36,289	[1]	17,786	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(1,389)	[1]	(543)	[2]
Marketable Securities Fair Value 12 Months or Longer	10,217	[1]	10,633	[2]
Marketable Securities Unrealized Losses 12 months or longer	(528)	[1]	(364)	[2]
Marketable Securities Fair Value Total	46,506	[1]	28,419	[2]
Marketable Securities Unrealized Losses Total	(1,917)	[1]	(907)	[2]
Number of investable securities	113		65
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	34,564	[1]	14,183	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(1,199)	[1]	(134)	[2]
Marketable Securities Fair Value 12 Months or Longer	10,217	[1]	10,633	[2]
Marketable Securities Unrealized Losses 12 months or longer	(528)	[1]	(364)	[2]
Marketable Securities Fair Value Total	44,781	[1]	24,816	[2]
Marketable Securities Unrealized Losses Total	(1,727)	[1]	(498)	[2]
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	3,291	[1]	1,792	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(151)	[1]	(5)	[2]
Marketable Securities Fair Value 12 Months or Longer	171	[1]	416	[2]
Marketable Securities Unrealized Losses 12 months or longer	(4)	[1]	(9)	[2]
Marketable Securities Fair Value Total	3,462	[1]	2,208	[2]
Marketable Securities Unrealized Losses Total	(155)	[1]	(14)	[2]
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	12,374	[1]	6,633	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(454)	[1]	(79)	[2]
Marketable Securities Fair Value 12 Months or Longer	6,229	[1]	4,457	[2]
Marketable Securities Unrealized Losses 12 months or longer	(309)	[1]	(114)	[2]
Marketable Securities Fair Value Total	18,603	[1]	11,090	[2]
Marketable Securities Unrealized Losses Total	(763)	[1]	(193)	[2]
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	16,051	[1]	5,306	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(513)	[1]	(39)	[2]
Marketable Securities Fair Value 12 Months or Longer	3,487	[1]	5,760	[2]
Marketable Securities Unrealized Losses 12 months or longer	(198)	[1]	(241)	[2]
Marketable Securities Fair Value Total	19,538	[1]	11,066	[2]
Marketable Securities Unrealized Losses Total	(711)	[1]	(280)	[2]
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	2,848	[1]	452	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(81)	[1]	(11)	[2]
Marketable Securities Fair Value 12 Months or Longer	330	[1]	0	[2]
Marketable Securities Unrealized Losses 12 months or longer	(17)	[1]	0	[2]
Marketable Securities Fair Value Total	3,178	[1]	452	[2]
Marketable Securities Unrealized Losses Total	(98)	[1]	(11)	[2]
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	1,725	[1]	3,603	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(190)	[1]	(409)	[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	1,725	[1]	3,603	[2]
Marketable Securities Unrealized Losses Total	$ (190)	[1]	$ (409)	[2]

[1] Includes approximately 113 securities.

[2] Includes approximately 65 securities.