Debt - Additional Information 3 (Detail) (USD $)					1 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended			1 Months Ended		1 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Apr. 18, 2013 2011 Term Loan B [Member]	Apr. 18, 2013 2012-2 Term Loan B [Member]	Apr. 16, 2010 4.254% Secured Tower Revenue Securities Series 2010-1 [Member]	Sep. 30, 2013 4.254% Secured Tower Revenue Securities Series 2010-1 [Member]	Dec. 31, 2012 4.254% Secured Tower Revenue Securities Series 2010-1 [Member]	Apr. 16, 2010 5.101% Secured Tower Revenue Securities Series 2010-2 [Member]	Sep. 30, 2013 5.101% Secured Tower Revenue Securities Series 2010-2 [Member]	Dec. 31, 2012 5.101% Secured Tower Revenue Securities Series 2010-2 [Member]	Sep. 30, 2013 Tower Securities [Member]	Apr. 16, 2010 Tower Securities [Member]	Apr. 16, 2010 Commercial Mortgage Series 2006-1 [Member]	Sep. 30, 2013 Revolving Credit Facility [Member]	Apr. 18, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Sep. 30, 2013 2012-1 Tower Securities [Member]	Aug. 09, 2012 2012-1 Tower Securities [Member]	Apr. 18, 2013 2013-1C Tower Securities [Member]	Apr. 18, 2013 2013-2C Tower Securities [Member]	Apr. 18, 2013 2013-1DTower Securities [Member]	Sep. 30, 2013 2013 Tower Securities [Member]	Apr. 18, 2013 2013 Tower Securities [Member]
Line of Credit Facility [Line Items]
Proceeds from issuance of 2010 Tower Securities, net of fees paid					$ 680,000,000			$ 550,000,000
Securities, annual interest rate					4.254%			5.101%
Weighted average annual fixed coupon interest rate												4.70%
Tower revenue securities anticipated repayment date					2015-04-15			2017-04-17
Tower revenue securities maturity date					2040-04-16			2042-04-15
Line of credit facility, deferred financing fees											18,000,000						14,900,000					25,100,000
Repayment of debt													0
Face amount of debt	5,691,697,000	5,440,073,000				680,000,000	680,000,000		550,000,000	550,000,000						100,000,000		610,000,000	425,000,000	575,000,000	330,000,000		1,330,000,000
Debt instrument interest rate stated percentage						4.254%			5.101%									2.933%	2.24%	3.722%	3.598%		3.218%
Repayment date of debt instrument																			April 2018	April 2023	April 2018
Weighted average life of debt instrument through the anticipated repayment date																							7 years 2 months 12 days
Debt instrument, maturity date						Apr. 15, 2015			Apr. 17, 2017					May 09, 2017					Apr. 30, 2043	Apr. 30, 2048	Apr. 30, 2043
Outstanding amount			$ 310,700,000	$ 189,300,000											$ 100,000,000