Equity Based Compensation Plans, Summary information of stock options outstanding (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options outstanding, ending balance (in shares)	623,434
Options outstanding, weighted-average remaining contractual life	6 years 8 months 12 days
Options outstanding, weighted-average exercise price (in dollars per share)	125.96
Number of options exercisable, ending balance (in shares)	250,620
Options exercisable, weighted-average exercise price (in dollars per share)	107.12
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)	1,614	1,540	14,415
Unrecognized compensation cost, weighted average recognition period, minimum	1 year
Unrecognized compensation cost, weighted average recognition period, maximum	7 years
51.01 - 79.05 [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)	51.01
Exercise price range, upper range limit (in dollars per share)	79.05
Number of options outstanding, ending balance (in shares)	34,973
Options outstanding, weighted-average remaining contractual life	3 years
Options outstanding, weighted-average exercise price (in dollars per share)	69.97
Number of options exercisable, ending balance (in shares)	34,973
Options exercisable, weighted-average exercise price (in dollars per share)	69.97
79.25 - 125.84 [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)	79.25
Exercise price range, upper range limit (in dollars per share)	125.84
Number of options outstanding, ending balance (in shares)	144,498
Options outstanding, weighted-average remaining contractual life	3 years 10 months 24 days
Options outstanding, weighted-average exercise price (in dollars per share)	99.10
Number of options exercisable, ending balance (in shares)	130,498
Options exercisable, weighted-average exercise price (in dollars per share)	98.69
126.73 - 155.34 [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)	126.73
Exercise price range, upper range limit (in dollars per share)	155.34
Number of options outstanding, ending balance (in shares)	443,963
Options outstanding, weighted-average remaining contractual life	7 years 10 months 24 days
Options outstanding, weighted-average exercise price (in dollars per share)	139.10
Number of options exercisable, ending balance (in shares)	85,149
Options exercisable, weighted-average exercise price (in dollars per share)	135.31