Equity Based Compensation Plans Summary of stock options activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock options [Roll Forward]
Beginning balance, outstanding (in shares)	415,020	300,642	378,542
Granted (in shares)	263,113	197,500	18,214
Exercised (in shares)	(41,603)	(83,122)	(78,381)
Forfeited and canceled (in shares)	(13,096)	0	(17,733)
Ending balance, outstanding (in shares)	623,434	415,020	300,642
Options exercisable, ending balance (in shares)	250,620	219,820	265,770
Stock options additional disclosures [Abstract]
Weighted average exercise price, outstanding, beginning balance (in dollars per share)	$ 109.71	$ 88.11	$ 82.08
Weighted average exercise price, granted (in dollars per share)	$ 143.95	$ 131.87	$ 107.21
Weighted average exercise price, exercised (in dollars per share)	$ 77.21	$ 84.24	$ 63.97
Weighted average exercise price, forfeited and canceled (in dollars per share)	$ 128.36	$ 0.00	$ 105.40
Weighted average exercise price, outstanding, ending balance (in dollars per share)	$ 125.96	$ 109.71	$ 88.11
Weighted average exercise price, options exercisable, ending balance (in dollars per share)	$ 107.12	$ 92.31	$ 86.28