Segment Information (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue
Total revenues	$ 660,711	[1]	$ 641,520	[1]	$ 614,502	[1]	$ 568,566	[1]	$ 563,145	[2]	$ 554,691	[2]	$ 359,421	[2]	$ 266,396	[2]	$ 2,485,299	$ 1,743,653	$ 1,000,634
Net real estate property:
Net real estate property	17,111,532								15,913,732								17,111,532	15,913,732
United States
Revenue
Total revenues																	2,389,330	1,651,614	916,104
Net real estate property:
Net real estate property	16,711,508								15,510,824								16,711,508	15,510,824
Canada
Revenue
Total revenues																	95,969	92,039	84,530
Net real estate property:
Net real estate property	$ 400,024								$ 402,908								$ 400,024	$ 402,908

[1] The amounts presented for the three months ended March 31, 2012, June 30, 2012 and September 30, 2012 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 2012 or classified as held for sale as of December 31, 2012.

[2] The amounts presented for the three months ended March 31, 2011, June 30, 2011, September 30, 2011 and December 31, 2011 differ from the amounts previously reported in our Annual Report on Form 10-K for the year ended December 31, 2011 as a result of discontinued operations consisting of properties sold in 2012 or classified as held for sale as of December 31, 2012.