Stock Option and Incentive Plan (Outperformance Awards) (Narrative) (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2011 years	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 01, 2016	Feb. 01, 2015	Feb. 01, 2014
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
LTIP and common units equivalency ratio	one-for-one
Maximum [Member] | TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Cumulative absolute TRS hurdle	27.00%
Minimum [Member] | TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Cumulative absolute TRS hurdle	0.00%
TRS Component Sliding Scale One [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
TRS measurement, years	3
Cumulative absolute TRS hurdle	27.00%
Percentage of the potential relative TRS component earned if the Company's TRS is equal to or greater than a cumulative 27% over three years	100.00%
TRS Component Sliding Scale Two [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Cumulative absolute TRS hurdle, annum	0.00%
Percentage earned if the Company's TRS is 0% or less	0.00%
TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
TRS measurement, years	3
Percentage calculated by linear interpolation earned if the Company's cumulative TRS over three years is between 0% and 27%, minimum	0.00%
Percentage calculated by linear interpolation earned if the Company's cumulative TRS over three years is between 0% and 27%, maximum	100.00%
TRS Component Hypothetical Situation [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
TRS measurement, years	3
Cumulative absolute TRS hurdle	18.00%
Cumulative absolute TRS hurdle, annum	6.00%
Potential relative TRS component proration percentage	66.67%
OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
TRS measurement, years	3
Award additional vesting period, years	2
Measurement period for 2011 OPP Awards	February 1, 2011 to January 31, 2014
Average closing price of common stock for five trading days prior and including February 1, 2011	$ 93.38
Trading days prior to and including February 1, 2011	5
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	27.00%
Cumulative absolute TRS hurdle, annum	9.00%
Vesting percentage for 2011 OPP Awards					50.00%	25.00%	25.00%
Vesting date		Feb. 01, 2016	Feb. 01, 2015	Feb. 01, 2014
Performance measurement period, days	15
Distributions percent before measurement date	10.00%