Equity Based Compensation Plans Summary of stock options activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shares [Roll Forward]
Beginning balance, outstanding	695,488	623,434	415,020
Granted	42,518	150,325	263,113
Assumed - Merger	133,766	0	0
Exercised	(185,387)	(52,970)	(41,603)
Forfeited and canceled	(21,600)	(25,301)	(13,096)
Ending balance, outstanding	664,785	695,488	623,434
Options exercisable at year end	395,986	300,632	250,620
Weighted-average exercise price [Abstract]
Outstanding at beginning of year (in dollars per share)	$ 133.37	$ 125.96	$ 109.71
Granted (in dollars per share)	$ 176.65	$ 153.54	$ 143.95
Assumed - Merger (in dollars per share)	$ 121.03	$ 0.00	$ 0.00
Exercised (in dollars per share)	$ 113.72	$ 102.43	$ 77.21
Forfeited and canceled (in dollars per share)	$ 144.29	$ 135.25	$ 128.36
Outstanding at end of year (in dollars per share)	$ 138.78	$ 133.37	$ 125.96
Options exercisable at year end (in dollars per share)	$ 133.99	$ 119.09	$ 107.12