Stock Option And Incentive Plan (Narrative) (Detail) (USD $)	9 Months Ended	0 Months Ended	9 Months Ended		1 Months Ended		9 Months Ended										0 Months Ended
	Sep. 30, 2012	Feb. 13, 2012 Executive Vice President [Member] M Y	Sep. 30, 2012 Executive Vice President [Member]	Feb. 13, 2012 2011 Outperformance Award [Member] Executive Vice President [Member]	Feb. 07, 2012 OPP Units 2012 [Member] D	Jan. 25, 2012 OPP Units 2012 [Member] Y	Sep. 30, 2012 OPP Units 2012 [Member] D Y	Sep. 30, 2012 OPP Units 2012 [Member] OPP Awards Vesting 2015 [Member]	Sep. 30, 2012 OPP Units 2012 [Member] OPP Awards Vesting 2016 [Member]	Sep. 30, 2012 OPP Units 2012 [Member] Opp Awards Vesting 2017 [Member]	Sep. 30, 2012 TRS Component Sliding Scale One [Member] Y	Sep. 30, 2012 TRS Component Sliding Scale Two [Member]	Sep. 30, 2012 TRS Component Sliding Scale Three [Member] Y	Sep. 30, 2012 TRS Component Sliding Scale Three [Member] Minimum [Member]	Sep. 30, 2012 TRS Component Sliding Scale Three [Member] Maximum [Member]	Sep. 30, 2012 TRS Component Hypothetical Situation [Member] Y	May 15, 2012 2012 Stock Option And Incentive Plan [Member] Y
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
TRS measurement, years						3					3		3			3
Award additional vesting period, years						2
Trading days prior to and including February 7, 2012					5
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
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%				24.00%			0.00%	24.00%	18.00%
Cumulative absolute TRS hurdle, annum							8.00%					0.00%				6.00%
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%												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%
Vesting Percentage								25.00%	25.00%	50.00%
Vesting Date								Feb. 07, 2015	Feb. 07, 2016	Feb. 07, 2017
Performance measurement period, days							15
Distributions percent before measurement date							10.00%
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
Maximum number of shares of common stock, Authorized shares																	13,000,000
Other than stock options awards conversion ratio																	2.32
Stock option awards conversion ratio																	1.0
Stock option and incentive plan term period																	10