Financial Instruments And Investments (Marketable Securities Fair Value And Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012 securities		Dec. 31, 2011 securities
Schedule of Available-for-sale Securities [Line Items]
Decommissioning Fund Investments	$ 178,528		$ 167,963
Marketable Securities Fair Value Less than 12 Months	16,481	[1]	17,103	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(1,091)	[1]	(2,223)	[2]
Marketable Securities Fair Value 12 Months or Longer	11,023	[1]	11,351	[2]
Marketable Securities Unrealized Losses 12 months or longer	(643)	[1]	(737)	[2]
Marketable Securities Fair Value Total	27,504	[1]	28,454	[2]
Marketable Securities Unrealized Losses Total	(1,734)	[1]	(2,960)	[2]
Number of investable securities	87		96
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	8,935	[1]	6,415	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(75)	[1]	(158)	[2]
Marketable Securities Fair Value 12 Months or Longer	9,412	[1]	9,611	[2]
Marketable Securities Unrealized Losses 12 months or longer	(287)	[1]	(248)	[2]
Marketable Securities Fair Value Total	18,347	[1]	16,026	[2]
Marketable Securities Unrealized Losses Total	(362)	[1]	(406)	[2]
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	20	[1]	515	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(1)	[1]	(8)	[2]
Marketable Securities Fair Value 12 Months or Longer	1,304	[1]	1,233	[2]
Marketable Securities Unrealized Losses 12 months or longer	(33)	[1]	(23)	[2]
Marketable Securities Fair Value Total	1,324	[1]	1,748	[2]
Marketable Securities Unrealized Losses Total	(34)	[1]	(31)	[2]
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	3,271	[1]	100	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(34)	[1]	(1)	[2]
Marketable Securities Fair Value 12 Months or Longer	2,395	[1]	2,413
Marketable Securities Unrealized Losses 12 months or longer	(56)	[1]	(38)	[2]
Marketable Securities Fair Value Total	5,666	[1]	2,513	[2]
Marketable Securities Unrealized Losses Total	(90)	[1]	(39)	[2]
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	3,310	[1]	2,275	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(26)	[1]	(31)	[2]
Marketable Securities Fair Value 12 Months or Longer	4,981	[1]	4,731	[2]
Marketable Securities Unrealized Losses 12 months or longer	(189)	[1]	(144)	[2]
Marketable Securities Fair Value Total	8,291	[1]	7,006	[2]
Marketable Securities Unrealized Losses Total	(215)	[1]	(175)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	2,334	[1]	3,525	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(14)	[1]	(118)	[2]
Marketable Securities Fair Value 12 Months or Longer	732	[1]	1,234	[2]
Marketable Securities Unrealized Losses 12 months or longer	(9)	[1]	(43)	[2]
Marketable Securities Fair Value Total	3,066	[1]	4,759	[2]
Marketable Securities Unrealized Losses Total	(23)	[1]	(161)	[2]
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities Fair Value Less than 12 Months	7,546	[1]	10,688	[2]
Marketable Securities Unrealized Losses Less than 12 Months	(1,016)	[1]	(2,065)	[2]
Marketable Securities Fair Value 12 Months or Longer	1,611	[1]	1,740	[2]
Marketable Securities Unrealized Losses 12 months or longer	(356)	[1]	(489)	[2]
Marketable Securities Fair Value Total	9,157	[1]	12,428	[2]
Marketable Securities Unrealized Losses Total	$ (1,372)	[1]	$ (2,554)	[2]

[1] Includes approximately 87 securities

[2] (2)Includes approximately 96 securities