Segment Information (Geographic Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue
Total revenues	$ 732,856	[1]	$ 710,924	[1]	$ 683,764	[1]	$ 682,509	[1]	$ 655,730	[2]	$ 637,218	[2]	$ 610,188	[2]	$ 564,597	[2]	$ 2,810,053	$ 2,467,733	$ 1,731,704
Net real estate property:
Net real estate property	18,075,586								17,111,532								18,075,586	17,111,532
United States
Revenue
Total revenues																	2,716,835	2,371,764	1,639,665
Net real estate property:
Net real estate property	17,705,962								16,711,508								17,705,962	16,711,508
Canada
Revenue
Total revenues																	93,218	95,969	92,039
Net real estate property:
Net real estate property	$ 369,624								$ 400,024								$ 369,624	$ 400,024

[1] The amounts presented for the three months ended March 31, 2013, June 30, 2013 and September 30, 2013 differ from the amounts previously reported in our Quarterly Reports on Form 10-Q as a result of discontinued operations consisting of properties sold in 2013 or classified as held for sale as of December 31, 2013.

[2] The amounts presented for the three months ended March 31, 2012, June 30, 2012, September 30, 2012 and December 31, 2012 differ from the amounts previously reported in our Annual Report on Form 10-K for the year ended December 31, 2012 as a result of discontinued operations consisting of properties sold in 2013 or classified as held for sale as of December 31, 2013.