Equity Based Compensation Plans, Summary information of stock options outstanding (Details)	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options outstanding (in shares) | shares	525,094
Options outstanding, Weighted-average remaining contractual life (years)	5 years 9 months 18 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 154.98
Number of options exercisable (in shares) | shares	342,048
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 152.42
$62.34 - $101.01 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit (in dollars per share)	66.05
Exercise price range, upper range limit (in dollars per share)	$ 101.01
Number of options outstanding (in shares) | shares	15,901
Options outstanding, Weighted-average remaining contractual life (years)	3 years 2 months 12 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 74.47
Number of options exercisable (in shares) | shares	15,901
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 74.47
105.64 - 161.98 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit (in dollars per share)	105.64
Exercise price range, upper range limit (in dollars per share)	$ 161.98
Number of options outstanding (in shares) | shares	367,024
Options outstanding, Weighted-average remaining contractual life (years)	5 years 3 months 18 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 139.73
Number of options exercisable (in shares) | shares	218,041
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 135.00
164.76 - 179.48 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit (in dollars per share)	164.76
Exercise price range, upper range limit (in dollars per share)	$ 229.43
Number of options outstanding (in shares) | shares	142,169
Options outstanding, Weighted-average remaining contractual life (years)	7 years 6 months
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 203.37
Number of options exercisable (in shares) | shares	108,106
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 199.02