Stock-based Compensation (Details 1) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock Units RSU [Member]
Share Based Compensation Equity Instruments Other Than Stock Options And Restricted Stock Units Summary [Abstract]
Grant-Date Fair Value	$ 906,000	$ 1,048,000	$ 857,000
Share Based Compensation Equity Instruments Other Than Options Plan Activity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value, Beginning of Period	$ 78.32
Units Granted Weighted Average Grant Date Fair Value	110.84
Awards Vested Weighted Average Grant Date Fair Value	78.08
Units Cancelled or Expired Weighted Average Grant Date Fair Value	88.69
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value, End of Period	$ 91.09	$ 78.32
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Beginning Balance	24,478
Restricted Stock Granted Shares	8,177
Vested Units	(11,298)
Cancelled or Expired Units	(1,765)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance	19,592	24,478
Restricted Operating Partnership Units Plan [Member]
Share Based Compensation Equity Instruments Other Than Stock Options And Restricted Stock Units Summary [Abstract]
Grant-Date Fair Value	$ 20,293,000	$ 19,669,000	$ 31,947,000
Share Based Compensation Equity Instruments Other Than Options Plan Activity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value, Beginning of Period	$ 74.38
Units Granted Weighted Average Grant Date Fair Value	102.75
Awards Vested Weighted Average Grant Date Fair Value	74.22
Units Cancelled or Expired Weighted Average Grant Date Fair Value	83.89
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value, End of Period	$ 83.07	$ 74.38
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Beginning Balance	721,662
Restricted Stock Granted Shares	197,497
Vested Units	(270,443)
Cancelled or Expired Units	(9,699)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance	639,017	721,662
Employee Stock Option [Member]
Share Based Compensation Employee Stock Purchase Plan Activity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period	$ 60.82
Stock Options Granted Weighted Average Exercise Price	112.10
Stock Options Exercised Weighted Average Exercise Price	82.21
Stock Options Cancelled or Expired Weighted Average Exercise Price	100.21
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period	$ 60.06	$ 60.82
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Beginning Balance	2,965,968
Stock Options Granted Shares	35,208
Stock Options Exercised Shares	(160,266)
Stock Options Cancelled or Expired Shares	(13,340)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	2,827,570	2,965,968
Options Vested And Expected To Vest Shares	2,826,685
Options Vested And Expected To Vest Weighted Average Exercise Price	$ 60.06
Options Excercisable Shares	2,741,863
Options Excercisable Weighted Average Exercise Price	$ 59.08
Options Exercisable Weighted Average Remaining Contractual Term	3 years 9 months 18 days
Options Outstanding Weighted Average Remaining Contractual Term	4 years
Options Vested And Expected To Vest Weighted Average Remaining Contractual Term	4 years
Options Outstanding Aggregate Intrinsic Value (in US dollars)	$ 115,796,000
Options Vested And Expected To Vest Aggregate Intrinsic Value (in US dollars)	115,788,000
Options Excercisable Aggregate Intrinsic Value (in US dollars)	$ 114,653,000
Fair Value Assumptions Expected Volatility Rate	35.00%	36.00%	36.00%
Fair Value Assumptions Expected Life	5 years	5 years	5 years
Fair Value Assumptions Risk Free Interest Rate	1.56%	1.81%	0.91%
Fair Value Assumptions Risk Expected Dividend Yield (in percentage)	3.30%	4.10%	4.30%
Out Performance Plan 2015 [Member]
Share Based Compensation Equity Instruments Other Than Stock Options And Restricted Stock Units Summary [Abstract]
Out of performance plan notional amount	$ 40,000,000
Grant-Date Fair Value	$ 9,120,000
OPP Units Earned, String	To be determined in 2017
Out Performance Plan 2014 [Member]
Share Based Compensation Equity Instruments Other Than Stock Options And Restricted Stock Units Summary [Abstract]
Out of performance plan notional amount	$ 50,000,000
Grant-Date Fair Value	$ 8,202,000
OPP Units Earned, String	To be determined in 2016
Out Performance Plan 2013 [Member]
Share Based Compensation Equity Instruments Other Than Stock Options And Restricted Stock Units Summary [Abstract]
Out of performance plan notional amount	$ 40,000,000
Grant-Date Fair Value	$ 6,814,000
OPP Units Earned	85,420
Out Performance Plan 2012 [Member]
Share Based Compensation Equity Instruments Other Than Stock Options And Restricted Stock Units Summary [Abstract]
Out of performance plan notional amount	$ 40,000,000
Grant-Date Fair Value	$ 12,250,000
OPP Units Earned	303,202