Debt (Secured Tower Revenue Securities) (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended			0 Months Ended		9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended			9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended				9 Months Ended	0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Oct. 15, 2014 4.254% 2010-1 Tower Securities [Member]	Apr. 16, 2010 4.254% 2010-1 Tower Securities [Member]	Sep. 30, 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]	Sep. 30, 2014 5.101% 2010-2 Tower Securities [Member]	Dec. 31, 2013 5.101% 2010-2 Tower Securities [Member]	Oct. 15, 2014 2010 Secured Tower Revenue Securities [Member]	Apr. 16, 2010 2010 Secured Tower Revenue Securities [Member]	Aug. 09, 2012 2.933% 2012-1 Tower Securities [Member]	Sep. 30, 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]	Sep. 30, 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]	Sep. 30, 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]	Sep. 30, 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]	Oct. 15, 2014 2.898% 2014-1C Tower Securities [Member]	Oct. 15, 2014 3.869% 2014-2C Tower Securities [Member]	Oct. 15, 2014 2014 Secured Tower Revenue Securities [Member]	Sep. 30, 2014 2014 Secured Tower Revenue Securities [Member]	Oct. 15, 2014 Revolving Credit Facility [Member]	Sep. 30, 2014 Revolving Credit Facility [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Apr. 29, 2009 4.0% Convertible Senior Notes [Member]	Sep. 30, 2014 4.0% Convertible Senior Notes [Member]	Dec. 31, 2013 4.0% Convertible Senior Notes [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	$ 920,000,000	$ 620,000,000
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%			2.898%	3.869%						4.00%	4.00%
Debt instrument, weighted average interest rate														4.70%													3.218%			3.289%
Repayment date of debt instrument							Apr. 15, 2015			Apr. 17, 2017					Dec. 15, 2017			Apr. 16, 2018			Apr. 17, 2023			Apr. 16, 2018				Oct. 15, 2019	Oct. 15, 2024
Debt instrument, maturity date							Apr. 16, 2040	Apr. 15, 2015		Apr. 15, 2042	Apr. 17, 2017				Dec. 15, 2042	Dec. 15, 2017		Apr. 15, 2043	Apr. 16, 2018		Apr. 15, 2048	Apr. 17, 2023		Apr. 15, 2043	Apr. 16, 2018			Oct. 17, 2044	Oct. 15, 2049				May 09, 2017		Oct. 01, 2014	Oct. 01, 2014
Amortized deferred financing fees	4,599,000	3,981,000	13,114,000	11,508,000									1,100,000	18,000,000	14,900,000												25,500,000				20,900,000
Weighted average life of debt instrument through the anticipated repayment date																											7 years 2 months 12 days			7 years
Aggregate debt	7,550,088,000		7,550,088,000		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				1,540,000,000			300,000,000	215,000,000		367,068,000	468,394,000
Repayments of long-term debt						$ 680,000,000																										$ 300,000,000