Stock Option And Incentive Plan (Narrative) (Details) (USD $)	3 Months Ended					12 Months Ended	0 Months Ended		3 Months Ended						0 Months Ended	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 TRS Component Sliding Scale One [Member] Y	Mar. 31, 2012 TRS Component Sliding Scale Two [Member]	Mar. 31, 2012 TRS Component Sliding Scale Three [Member] Y	Mar. 31, 2012 TRS Component Hypothetical Situation [Member] Y	Dec. 31, 2011 OPP Units 2008 [Member]	Feb. 07, 2012 OPP Units 2012 [Member] D	Jan. 25, 2012 OPP Units 2012 [Member] Y	Mar. 31, 2012 OPP Units 2012 [Member] D	Mar. 31, 2012 OPP Awards Vesting 2015 [Member] OPP Units 2012 [Member]	Mar. 31, 2012 OPP Awards Vesting 2016 [Member] OPP Units 2012 [Member]	Mar. 31, 2012 Opp Awards Vesting 2017 [Member] OPP Units 2012 [Member]	Mar. 31, 2012 Minimum [Member] TRS Component Sliding Scale Three [Member]	Mar. 31, 2012 Maximum [Member] TRS Component Sliding Scale Three [Member]	Feb. 13, 2012 Executive Vice President [Member] Y M	Mar. 31, 2012 Executive Vice President [Member]	Feb. 13, 2012 2011 Outperformance Award [Member] Executive Vice President [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Award additional vesting period, years								2
Measurement Period For Outperformance Awards									February 7, 2012 to February 6, 2015
Start of the measurement period									Feb. 07, 2012
End of the measurement period									Feb. 06, 2015
Trading days prior to and including February 7, 2012							5
TRS measurement, years		3		3	3	3		3
Average closing price of common stock for five trading days prior and including February 7, 2012							$ 106.69
Aggregate rewards of OPP awards, maximum cap									$ 40,000,000
Excess total return above a cumulative absolute TRS hurdle									2.00%
Cumulative absolute TRS hurdle		24.00%			18.00%				24.00%				0.00%	24.00%
Cumulative absolute TRS hurdle, annum			0.00%		6.00%				8.00%
Measurement period for cumulative absolute TRS hurdle (years)									3
Excess or deficient total return of relative TRS hurdle equal to total return of REIT Index									2.00%
Percentage of the potential relative TRS component earned if the Company's TRS is equal to or greater than a cumulative 24% over three years		100.00%
Percentage earned if the Company's TRS is 0% or less			0.00%
Percentage calculated by linear interpolation earned if the Company's cumulative TRS over three years is between 0% and 24%, minimum				0.00%
Percentage calculated by linear interpolation earned if the Company's cumulative TRS over three years is between 0% and 24%, maximum				100.00%
Potential relative TRS component proration percentage					75.00%
Distributions percent before measurement date									10.00%
Vesting Percentage										25.00%	25.00%	50.00%
Vesting Date										Feb. 07, 2015	Feb. 07, 2016	Feb. 07, 2017
Performance measurement period, days									15
LTIP And Common Units Equivalency Ratio	one-for-one
Cash payment related to resignation															1,533,333
Cash bonus for 2011 as part of resignation agreement															950,000
Consulting period, months															2
Consulting fee, per month															20,000
Accelerated share vesting with respect to LTIP units															23,502
Common shares received due to accelerated share vesting with respect to stock options															4,464
Accelerated share vesting with respect to common stock															5,117
Common stock exercise price per share for stock options															$ 92.71
Common stock exercise price per share for common stock															$ 104.47
Percentage of outperformance award retained																	36.00%
Non-compete agreement, years															1
Expense recognized upon resignation																$ 4,500,000