Senior Unsecured Notes and Secured Debt (Details) In Thousands, unless otherwise specified	3 Months Ended		3 Months Ended						3 Months Ended
	Mar. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Mar. 31, 2013 Senior Unsecured Notes [Member] USD ($)		Mar. 31, 2013 Secured Debt [Member] USD ($)		Mar. 31, 2013 Canadian Denominated Unsecured Term Loan [Member] USD ($)	Jul. 30, 2012 Canadian Denominated Unsecured Term Loan [Member] CAD	Mar. 31, 2013 Unsecured Line of Credit Term Loan [Member] USD ($)
Principal payments due on debt obligations
2013	$ 400,367		$ 300,000	[1],[2]	$ 100,367	[1],[3]
2014	278,237		0	[1],[2]	278,237	[1],[3]
2015	720,331		495,724	[1],[2],[4]	224,607	[1],[3]
2016	1,528,865		1,200,000	[1],[2]	328,865	[1],[3]
2017	770,537		450,000	[1],[2]	320,537	[1],[3]
Thereafter	5,366,823		4,194,403	[1],[2]	1,172,420	[1],[3]
Totals	9,065,160		6,640,127	[1],[2]	2,425,033	[1],[3]
Senior Unsecured Notes and Secured Debt (Textual) [Abstract]
Notes, annual stated interest rates, Minimum			3.00%		0.40%
Notes, annual stated interest rates, Maximum			6.50%		8.00%
Interest rate							2.65%		1.38%
Senior unsecured notes	6,610,873	6,114,151					245,724	250,000	500,000
Secured debt	2,452,495	2,336,196
Carrying values of properties securing the debt	$ 4,157,430
Interest Rate margin	1.175%						1.45%		1.35%
Debt instrument maturity date	Mar. 31, 2017						Jul. 27, 2015		Mar. 31, 2016

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

[2] (2) Annual interest rates range from 3.0% to 6.5%, excluding the Canadian denominated unsecured term loan discussed in footnote 4 and the $500,000,000 unsecured term loan discussed below.

[3] (3) Annual interest rates range from 0.4% to 8.0%. Carrying value of the properties securing the debt totaled $4,157,430,000 at March 31, 2013.

[4] (4) On July 30, 2012, we completed funding on a $250,000,000 Canadian denominated unsecured term loan (approximately $245,724,000 USD at exchange rates on March 31, 2013). The loan matures 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 (2.65% at March 31, 2013).