Long-Term Debt (Senior Unsecured Debt) (Details) (USD $) In Thousands, unless otherwise specified			9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended						9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended				9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended			9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Senior Note Due 3/15/2015 [Member]	Apr. 10, 2013 Senior Note Due 3/15/2015 [Member]	Sep. 30, 2013 Senior Note Due 4/15/2015 [Member]	Apr. 10, 2013 Senior Note Due 4/15/2015 [Member]	Sep. 30, 2013 Senior Note Due 4/15/2017 [Member]	Apr. 24, 2013 Senior Note Due 4/15/2017 [Member]	Sep. 30, 2013 Senior Note Due 10/1/2018 [Member]	Jun. 30, 2013 Senior Note Due 10/1/2018 [Member]	Sep. 30, 2013 Senior Note Due 4/15/2020 [Member]	Jun. 30, 2013 Senior Note Due 4/15/2020 [Member]	Sep. 30, 2013 Senior Unsecured Debt [Member]		Dec. 31, 2012 Senior Unsecured Debt [Member]		Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 1/15/2013 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 1/15/2013 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 5/1/2014 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 5/1/2014 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 3/15/2015 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 3/15/2015 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2015 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2015 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 10/14/2016 [Member]		Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 10/14/2016 [Member]		Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2017 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2017 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 10/1/2018 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 10/1/2018 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 3/15/2019 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 3/15/2019 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2020 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2020 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 7/1/2021 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 7/1/2021 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2022 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2022 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 1/15/2023 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 1/15/2023 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 4/15/2024 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 11/1/2025 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 11/1/2025 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 8/15/2026 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 8/15/2026 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 1/15/2027 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 1/15/2027 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 8/15/2031 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Senior Note Due 8/15/2031 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 10/1/2034 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 10/1/2034 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 7/1/2035 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 7/1/2035 [Member]	Sep. 30, 2013 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 10/1/2046 [Member]	Dec. 31, 2012 Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Debenture Due 10/1/2046 [Member]	Sep. 30, 2013 Subsidiary Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Subsidiary Senior Note Due 2/15/2028 [Member]	Dec. 31, 2012 Subsidiary Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Subsidiary Senior Note Due 2/15/2028 [Member]	Sep. 30, 2013 Subsidiary Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Subsidiary Senior Note Due 10/15/2029 [Member]	Dec. 31, 2012 Subsidiary Senior Notes And Debentures [Member] Senior Unsecured Debt [Member] Subsidiary Senior Note Due 10/15/2029 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 8,144,020	$ 8,942,568											$ 8,121,441		$ 8,919,696		$ 7,871,441	$ 8,669,696		$ 502,658	$ 200,000	$ 200,000	$ 105,026	$ 300,000	$ 96,872	$ 374,803	$ 474,375	[1]	$ 517,500	[1]	$ 606,874	$ 1,040,685	$ 582,739	$ 600,000	$ 434,000	$ 434,000	$ 1,021,505	$ 1,100,000	$ 500,000	$ 500,000	$ 500,000	$ 500,000	$ 850,000	$ 850,000	$ 750,000	$ 138,000	$ 138,000	$ 1,739	$ 1,739	$ 345,858	$ 345,858	$ 945,325	$ 945,325	$ 628	$ 628	$ 125,000	$ 125,000	$ 193,500	$ 193,500	$ 200,000	$ 200,000	$ 50,000	$ 50,000
Interest Rate				6.625%		7.875%		8.25%		8.125%		8.50%								6.25%	8.25%	8.25%	6.625%	6.625%	7.875%	7.875%	3.055%	[1]	3.095%	[1]	8.25%	8.25%	8.125%	8.125%	7.125%	7.125%	8.50%	8.50%	9.25%	9.25%	8.75%	8.75%	7.125%	7.125%	7.625%	7.00%	7.00%	6.80%	6.80%	7.875%	7.875%	9.00%	9.00%	7.68%	7.68%	7.45%	7.45%	7.05%	7.05%	6.73%	6.73%	8.40%	8.40%
Weighted average interest rate													7.77%	[2]	7.69%	[2]
Debt instrument, maturity date			Mar. 15, 2015		Apr. 15, 2015		Apr. 15, 2017		Oct. 01, 2018		Apr. 15, 2020		Oct. 14, 2016						Jan. 15, 2013		May 01, 2014		Mar. 15, 2015		Apr. 15, 2015		Oct. 14, 2016	[1]			Apr. 15, 2017		Oct. 01, 2018		Mar. 15, 2019		Apr. 15, 2020		Jul. 01, 2021		Apr. 15, 2022		Jan. 15, 2023		Apr. 15, 2024	Nov. 01, 2025		Aug. 15, 2026		Jan. 15, 2027		Aug. 15, 2031		Oct. 01, 2034		Jul. 01, 2035		Oct. 01, 2046		Feb. 15, 2028		Oct. 15, 2029

[1] Represents borrowings under the Credit Agreement with CoBank.

[2] Interest rate represents a weighted average of the stated interest rates of multiple issuances.