Senior Unsecured Notes and Secured Debt (Details)	12 Months Ended
	Dec. 31, 2013 USD ($)		Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2013 Senior Unsecured Notes [Member] USD ($)		Dec. 31, 2010 Senior Unsecured Notes [Member] USD ($)	Dec. 31, 2013 Secured Debt [Member] USD ($)		Dec. 31, 2013 Canadian Term Loan [Member] USD ($)	Dec. 31, 2013 Canadian Term Loan [Member] CAD	Dec. 31, 2013 Unsecured Term Loan [Member] USD ($)	Dec. 31, 2013 Unsecured Notes England [Member] USD ($)	Dec. 31, 2013 Unsecured Notes England [Member] GBP (£)
Principal payments due on debt obligations
2014	$ 330,295,000					$ 0	[1],[2]		$ 330,295,000	[1],[3]
2015	894,268,000	[4]				485,029,000	[1],[2],[4]		409,239,000	[1],[3],[4]
2016	1,582,917,000	[5]				1,200,000,000	[1],[2],[5]		382,917,000	[1],[3],[5]
2017	774,110,000					450,000,000	[1],[2]		324,110,000	[1],[3]
2018	879,284,000					450,000,000	[1],[2]		429,284,000	[1],[3]
Thereafter	5,971,544,000	[6]				4,836,678,000	[1],[2],[6]		1,134,866,000	[1],[3],[6]
Totals	10,432,418,000					7,421,707,000	[1],[2]		3,010,711,000	[1],[3]
Senior Unsecured Convertible Notes Issued [Abstract]
Convertible Debt Issued Amount					494,403,000
Interest rate on convertible debt issued					3.00%
Proceeds from issuance of senior unsecured convertible notes					486,084,000	219,925,000
Conversion rate of senior unsecured convertible notes					19.5064
Conversion price of senior unsecured convertible notes					$ 51.27
Equity component of convertible debt, reacquire	(555,000)			0				29,925,000
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Notes, annual stated interest rates, Minimum						1.50%			1.00%
Notes, annual stated interest rates, Maximum						6.50%			8.00%
Secured debt	3,058,248,000		2,336,196,000
Carrying values of properties securing the debt	6,243,475,000
Unsecured debt	7,379,308,000		6,114,151,000								235,029,000	250,000,000	500,000,000	911,570,000	550,000,000
Applicable margin over index, based on certain debt ratings	1.175%										1.35%	1.35%	1.35%
Senior note conversions	988,007		1,039,721
Loss (gain) on extinguishment of senior unsecured convertible notes	$ 909,000		$ 775,000	$ 979,000		$ 2,423,000
Interest Rate											2.70%	2.70%	1.50%	4.80%	4.80%
Maturity Date	Mar. 31, 2017										Jul. 27, 2015	Jul. 27, 2015	Mar. 31, 2016

[1] Amounts represent principal amounts due and do not include unamortized premiums/discounts or other fair value adjustments as reflected on the consolidated balance sheet.

[2] Annual interest rates range from 1.5% to 6.5%.

[3] Annual interest rates range from 1.0% to 8.0%. Carrying value of the properties securing the debt totaled $6,243,475,000 at December 31, 2013.

[4] On July 30, 2012, we completed funding on a $250,000,000 Canadian denominated unsecured term loan (approximately $235,029,000 based on the Canadian/U.S. Dollar exchange rate on December 31, 2013). The loan matures on July 27, 2015 (with an option to extend for an additional year at our discretion) and bears interest at the Canadian Dealer Offered Rate plus 145 basis points (2.7% at December 31, 2013).

[5] On January 8, 2013, we completed funding on a $500,000,000 unsecured term loan. The loan matures on March 31, 2016 (with an option to extend for two additional years at our discretion) and bears interest at LIBOR plus 135 basis points (1.5% at December 31, 2013).

[6] On November 20, 2013, we completed funding on a £550,000,000 (approximately $911,570,000 based on the Sterling/U.S. Dollar exchange rate on December 31, 2013) of 4.8% senior unsecured notes due 2028.