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Quarterly Financial Information (Unaudited) (Details) (USD $)
In Thousands, except Per Share data, 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
Quarterly Financial Data [Abstract]                      
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
Income from continuing operations attributable to common stockholders 97,992 [1] 115,975 [1] 43,496 [1] 48,110 [1] 193,553 [2] 103,191 [2] 18,450 [2] 47,939 [2] 305,573 363,133 213,444
Discontinued operations (11,725) [1] (4,093) [1] 30,529 [1] 42,516 [1] (605) [2] (306) [2] 1,226 [2] 1,045 [2] 57,227 1,360 32,723
Net income attributable to common stockholders $ 86,267 $ 111,882 $ 74,025 $ 90,626 $ 192,948 $ 102,885 $ 19,676 $ 48,984 $ 362,800 $ 364,493 $ 246,167
Basic:                      
Income from continuing operations attributable to common stockholders (in dollars per share) $ 0.33 $ 0.39 $ 0.15 $ 0.16 $ 0.67 $ 0.36 $ 0.10 $ 0.30 $ 1.04 $ 1.59 $ 1.36
Discontinued operations (in dollars per share) $ (0.04) $ (0.01) $ 0.11 $ 0.15 $ 0.00 $ 0.00 $ 0.01 $ 0.01 $ 0.20 $ 0.01 $ 0.21
Net income attributable to common stockholders (in dollars per share) $ 0.29 $ 0.38 $ 0.26 $ 0.31 $ 0.67 $ 0.36 $ 0.11 $ 0.31 $ 1.24 $ 1.60 $ 1.57
Diluted:                      
Income from continuing operations attributable to common stockholders (in dollars per share) $ 0.33 $ 0.39 $ 0.15 $ 0.16 $ 0.66 $ 0.35 $ 0.10 $ 0.29 $ 1.04 $ 1.57 $ 1.35
Discontinued operations (in dollars per share) $ (0.04) $ (0.01) $ 0.10 $ 0.15 $ 0.00 $ 0.00 $ 0.01 $ 0.01 $ 0.19 $ 0.01 $ 0.21
Net income attributable to common stockholders (in dollars per share) $ 0.29 $ 0.38 $ 0.25 $ 0.31 $ 0.66 $ 0.35 $ 0.11 $ 0.30 $ 1.23 $ 1.58 $ 1.56
Dividends declared per common share (in dollars per share) $ 0.62 $ 0.62 $ 0.62 $ 0.62 $ 0.575 $ 0.4486 $ 0.7014 $ 0.575      
[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.