Share Based and Deferred Compensation (Details Textuals) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Stock Option [Member]	Jun. 30, 2011 Stock Option [Member]	Jun. 30, 2012 Stock Option [Member] Y	Jun. 30, 2011 Stock Option [Member]	Jun. 30, 2012 Restricted Share Awards [Member]	Jun. 30, 2011 Restricted Share Awards [Member]	Jun. 30, 2012 Restricted Share Awards [Member] Age Y	Jun. 30, 2011 Restricted Share Awards [Member]	Jun. 30, 2012 Restricted Performance Share Units Plan [Member]	Jun. 30, 2011 Restricted Performance Share Units Plan [Member]	Jun. 30, 2012 Restricted Performance Share Units Plan [Member]	Jun. 30, 2011 Restricted Performance Share Units Plan [Member]	Apr. 02, 2009 Restricted Performance Share Units Plan [Member]	Jun. 30, 2012 Employee Share Purchase Plan [Member]	Jun. 30, 2011 Employee Share Purchase Plan [Member]	Jun. 30, 2012 Employee Share Purchase Plan [Member]	Jun. 30, 2011 Employee Share Purchase Plan [Member]	Jun. 30, 2012 Deferred Compensation Plan [Member]	Jun. 30, 2011 Deferred Compensation Plan [Member]	Mar. 01, 2012 Executive Officer [Member] Restricted Share Awards [Member]	Mar. 01, 2012 Executive Officer [Member] Restricted Performance Share Units Plan [Member]	Mar. 02, 2011 Executive Officer [Member] Restricted Performance Share Units Plan [Member]	Mar. 04, 2010 Executive Officer [Member] Restricted Performance Share Units Plan [Member]
Share Based and Deferred Compensation (Textuals) [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	3,483,537		3,483,537		3,599,672	3,483,537		3,483,537
Unvested options						671,783		671,783
Unrecognized compensation expenses						$ 1,600,000		$ 1,600,000		$ 4,700,000		$ 4,700,000
Weighted average period over which options will be recognized								1.3				2.6
Stock-based compensation expense, capitalized	500,000	400,000	900,000	700,000		400,000	400,000	700,000	700,000	200,000	100,000	300,000	300,000	200,000	100,000	400,000	200,000
Recognized compensation expense awards nominal amounts capitalized						100,000	100,000	200,000	200,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period												three to seven years from the initial grant date				3 years
Compensation expense recognized	1,900,000	1,600,000	3,600,000	3,300,000						800,000	800,000	1,500,000	1,600,000	700,000	500,000	1,300,000	800,000				100,000	100,000
Vesting Period, Minimum												3 Years
Vesting Period, Maximum												7 Years
Aggregate share-based awards awarded to executives																			1,250,000		1,250,000				194,858	262,713	123,107	119,766
Measurement period index percentage, minimum																										50.00%
Measurement period index percentage remaining amount compared to total shareholder return of Real Estate Investment Trusts within proxy peer group																										50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Cliff Vesting, Minimum												3 years
Voluntary termination of employment terms												after reaching age 57 and accumulating at least 15 years of service with the Company				after reaching age 57 and accumulating at least 15 years of service with the Company
Age limit of voluntary termination of employment												57
Accumulated Service Period For Voluntary Termination												15 years				15 years
Maximum number of shares to be delivered at the end of the measurement period relative to the total shareholder return																equal a certain percentage (not to exceed 200%) of the participant's base units
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Delivered																		372,102
Maximum percentage of the participant's base units																200.00%
Fair value of awards on the grant date																4,200,000	2,000,000
Share purchases made by employees under ESPP																					85% of the average closing price per share for a specified period
Share purchases made by employees under ESPP, Percentage																					85.00%
Percentage of plan contribution																					20.00%
Amount of participant contribution																					50,000
Purchase price of shares purchased under ESPP																			$ 100,000	$ 100,000	$ 200,000	$ 200,000
Deferred Compensation Arrangement With Individual Increase In Compensation Expense																							600,000	400,000
Deferred Compensation Arrangement With Individual Decrease In Compensation Expense																							$ 400,000	$ 400,000
Number of shares to be issued under deferred compensation plan included in total shares outstanding																							300,000	300,000