Share Based and Deferred Compensation (Details Textuals) (USD $)	3 Months Ended										3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Stock Option [Member] Y	Mar. 31, 2011 Stock Option [Member]	Mar. 31, 2012 Restricted Share Awards [Member] Age Y	Mar. 31, 2011 Restricted Share Awards [Member]	Mar. 31, 2012 Restricted Performance Share Units Plan [Member]	Mar. 31, 2011 Restricted Performance Share Units Plan [Member]	Mar. 31, 2010 Restricted Performance Share Units Plan [Member]	Apr. 02, 2009 Restricted Performance Share Units Plan [Member]	Mar. 31, 2012 Employee Share Purchase Plan [Member]	Mar. 31, 2012 Deferred Compensation Plan [Member]	Mar. 31, 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]
Unvested options			903,066
Unrecognized compensation expenses			$ 2,000,000		$ 5,100,000
Weighted average period over which options will be recognized			1.2		1.6
Stock-based compensation expense, capitalized	400,000	300,000	400,000	300,000	200,000	100,000	600,000	300,000	200,000
Recognized compensation expense awards nominal amounts capitalized			100,000
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	1,700,000	1,600,000			700,000	800,000
Vesting Period, Minimum					3 Years
Vesting Period, Maximum					7 Years
Aggregate share-based awards awarded to executives											1,250,000			196,719	265,222	124,293	120,955
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
Deferred Compensation Arrangement With Individual Increase In Compensation Expense												500,000	900,000
Deferred Compensation Arrangement With Individual Decrease In Compensation Expense												$ (400,000)	$ (900,000)
Number of shares to be issued under deferred compensation plan included in total shares outstanding												300,000	300,000