Stock Option and Incentive Plan Schedule of Stock Options Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	540,441	547,129	547,129	553,312
Outstanding, Weighted Average Exercise Price	$ 96.35	$ 96.38	$ 96.38	$ 97.21
Number Exercisable		514,360	465,371
Exercisable, Weighted Average Exercise Price		$ 96.32	$ 96.10
Exercise Price of $86.86 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	3 years 1 month 6 days
Number Outstanding at period end	118,502
Outstanding, Weighted Average Exercise Price	$ 86.86
Number Exercisable	118,502
Exercisable, Weighted Average Exercise Price	$ 86.86
Exercise Price of $95.69 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	5 years 3 months 18 days
Number Outstanding at period end	54,282
Outstanding, Weighted Average Exercise Price	$ 95.69
Number Exercisable	54,282
Exercisable, Weighted Average Exercise Price	$ 95.69
Exercise Price of $98.46 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	5 years 1 month 6 days
Number Outstanding at period end	202,030
Outstanding, Weighted Average Exercise Price	$ 98.46
Number Exercisable	202,030
Exercisable, Weighted Average Exercise Price	$ 98.46
Exercise Price of $100.77 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	4 years 1 month 6 days
Number Outstanding at period end	165,627
Outstanding, Weighted Average Exercise Price	$ 100.77
Number Exercisable	165,627
Exercisable, Weighted Average Exercise Price	$ 100.77
Unvested 2015 - 2017 MYLTIP Units [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted-average period (years)	2 years 3 months 18 days