Debt (Secured Tower Revenue Securities) (Narrative) (Details) (USD $)	3 Months Ended			0 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended		0 Months Ended		3 Months Ended		0 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended		0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Apr. 16, 2010 4.254% 2010-1 Tower Securities [Member]	Mar. 31, 2014 4.254% 2010-1 Tower Securities [Member]	Dec. 31, 2013 4.254% 2010-1 Tower Securities [Member]	Apr. 16, 2010 5.101% 2010-2 Tower Securities [Member]	Mar. 31, 2014 5.101% 2010-2 Tower Securities [Member]	Dec. 31, 2013 5.101% 2010-2 Tower Securities [Member]	Apr. 16, 2010 2010 Secured Tower Revenue Securities [Member]	Aug. 09, 2012 2.933% 2012-1 Tower Securities [Member]	Mar. 31, 2014 2.933% 2012-1 Tower Securities [Member]	Dec. 31, 2013 2.933% 2012-1 Tower Securities [Member]	Apr. 18, 2013 2.240% 2013-1C Tower Securities [Member]	Mar. 31, 2014 2.240% 2013-1C Tower Securities [Member]	Dec. 31, 2013 2.240% 2013-1C Tower Securities [Member]	Apr. 18, 2013 3.722% 2013-2C Tower Securities [Member]	Mar. 31, 2014 3.722% 2013-2C Tower Securities [Member]	Dec. 31, 2013 3.722% 2013-2C Tower Securities [Member]	Apr. 18, 2013 3.598% 2013-1D Tower Securities [Member]	Mar. 31, 2014 3.598% 2013-1D Tower Securities [Member]	Dec. 31, 2013 3.598% 2013-1D Tower Securities [Member]	Apr. 18, 2013 2013 Secured Tower Revenue Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 680,000,000			$ 550,000,000				$ 610,000,000			$ 425,000,000			$ 575,000,000			$ 330,000,000			$ 1,330,000,000
Debt instrument, interest rate, stated percentage				4.254%	4.254%		5.101%	5.101%			2.933%	2.933%		2.24%	2.24%		3.722%	3.722%		3.598%	3.598%
Debt instrument, weighted average interest rate										4.70%													3.218%
Repayment date of debt instrument				April 15, 2015			April 17, 2017				December 15, 2017			April 17, 2018			April 17, 2023			April 17, 2018
Debt instrument, maturity date				Apr. 16, 2040	Apr. 15, 2015		Apr. 15, 2042	Apr. 17, 2017			Dec. 15, 2042	Dec. 15, 2017		Apr. 17, 2043	Apr. 17, 2018		Apr. 17, 2048	Apr. 17, 2023		Apr. 17, 2043	Apr. 17, 2018
Amortized deferred financing fees	4,237,000	3,604,000								18,000,000	14,900,000												25,400,000
Weighted average life of debt instrument through the anticipated repayment date																							7 years 2 months 12 days
Aggregate debt	$ 6,869,758,000		$ 5,876,607,000		$ 680,000,000	$ 680,000,000		$ 550,000,000	$ 550,000,000			$ 610,000,000	$ 610,000,000		$ 425,000,000	$ 425,000,000		$ 575,000,000	$ 575,000,000		$ 330,000,000	$ 330,000,000