Condensed Quarterly Financial Information (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2010
Sep. 30, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Condensed Quarterly Financial Information [Abstract]                      
Total revenues $ 179,687 $ 177,155 $ 181,107 $ 186,330 $ 192,156 $ 197,956 $ 202,785 $ 194,583 $ 724,279 $ 787,480 $ 758,925
Operating and other expenses 69,844 62,661 69,921 75,966 67,913 73,089 70,394 70,668      
Direct construction costs 2,802 2,290 2,784 3,582 12,667 15,884 21,411 10,293 11,458 60,255 20,323
General and administrative 9,003 8,683 9,226 8,629 8,939 8,992 8,658 8,414 35,541 35,003 39,779
Depreciation and amortization 48,673 48,498 48,268 48,148 47,226 47,978 47,474 48,490 193,587 191,168 200,732
Impairment charge on rental property         9,521         9,521  
Total expenses 130,322 122,132 130,199 136,325 146,266 145,943 147,937 137,865 518,978 578,011 535,252
Operating income 49,365 55,023 50,908 50,005 45,890 52,013 54,848 56,718 205,301 209,469 223,673
Interest expense (31,784) (31,489) (31,363) (31,339) (35,982) (36,941) (37,335) (39,071) (125,975) (149,329) (140,068)
Interest and other investment income 9 10 10 10 13 34 18 21 39 86 570
Equity in earnings (loss) of unconsolidated joint ventures 848 539 736 (101) 2,063 475 260 (522) 2,022 2,276 (5,560)
Loss from early extinguishment of debt         (3,752)         (3,752)  
Gain on reduction of other obligations                             1,693
Total other (expense) income (30,927) (30,940) (30,617) (31,430) (37,658) (36,432) (37,057) (39,572) (123,914) (150,719) (143,365)
Income from continuing operations 18,438 24,083 20,291 18,575 8,232 15,581 17,791 17,146 81,387 58,750 80,308
Income (loss) from discontinued operations             11 231   242 (17)
Realized gains (losses) and unrealized losses on disposition of rental property, net             4,447     4,447  
Total discontinued operations, net             4,458 231   4,689 (16,580)
Net income 18,438 24,083 20,291 18,575 8,232 15,581 22,249 17,377 81,387 63,439 63,728
Noncontrolling interest in consolidated joint ventures 94 96 102 110 (19) 108 86 87 402 262 943
Noncontrolling interest in Operating Partnership (2,338) (3,015) (2,560) (2,456) (1,086) (2,150) (2,475) (2,422) (10,369) (8,133) (12,550)
Noncontrolling interest in discontinued operations             (635) (33)   (668) 2,447
Preferred stock dividends (72) (664) (500) (500) (500) (500) (500) (500) (1,736) (2,000) (2,000)
Net income available to common shareholders $ 16,122 $ 20,500 $ 17,333 $ 15,729 $ 6,627 $ 13,039 $ 18,725 $ 14,509 $ 69,684 $ 52,900 $ 52,568
Income from continuing operations $ 0.18 $ 0.24 $ 0.20 $ 0.19 $ 0.09 $ 0.16 $ 0.19 $ 0.18 $ 0.81 $ 0.62 $ 0.90
Discontinued operations             $ 0.05     $ 0.05 $ (0.19)
Net income available to common shareholders $ 0.18 $ 0.24 $ 0.20 $ 0.19 $ 0.09 $ 0.16 $ 0.24 $ 0.18 $ 0.81 $ 0.67 $ 0.71
Income from continuing operations $ 0.18 $ 0.24 $ 0.20 $ 0.19 $ 0.09 $ 0.16 $ 0.19 $ 0.18 $ 0.81 $ 0.62 $ 0.90
Discontinued operations             $ 0.05     $ 0.05 $ (0.19)
Net income available to common shareholders $ 0.18 $ 0.24 $ 0.20 $ 0.19 $ 0.09 $ 0.16 $ 0.24 $ 0.18 $ 0.81 $ 0.67 $ 0.71
Dividends declared per common share $ 0.45 $ 0.45 $ 0.45 $ 0.45 $ 0.45 $ 0.45 $ 0.45 $ 0.45 $ 1.80 $ 1.8 $ 1.8