Equity Based Compensation Plans, Summary information of stock options outstanding (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options outstanding (in shares)	695,488
Options outstanding, Weighted-average remaining contractual life (years)	6 years 9 months 18 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 133.37
Number of options exercisable (in shares)	300,632
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 119.09
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)	1,556	1,614	1,540
Unrecognized compensation cost, weighted average recognition period, minimum	1 year
Unrecognized compensation cost, weighted average recognition period, maximum	7 years
$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)	$ 62.34
Exercise price range, upper range limit (in dollars per share)	$ 101.01
Number of options outstanding (in shares)	74,261
Options outstanding, Weighted-average remaining contractual life (years)	2 years 8 months 12 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 79.18
Number of options exercisable (in shares)	72,261
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 79.02
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)	604,902
Options outstanding, Weighted-average remaining contractual life (years)	7 years 2 months 12 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 139.18
Number of options exercisable (in shares)	228,371
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 131.77
164.76 - 164.76 [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)	$ 164.76
Number of options outstanding (in shares)	16,325
Options outstanding, Weighted-average remaining contractual life (years)	9 years 4 months 24 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 164.76
Number of options exercisable (in shares)	0
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 0