Equity Based Compensation Plans Summary of stock options activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares [Roll Forward]
Beginning balance, outstanding	664,785	695,488	623,434
Granted	78,600	42,518	150,325
Assumed - Merger	0	133,766	0
Exercised	(203,556)	(185,387)	(52,970)
Forfeited and canceled	(14,735)	(21,600)	(25,301)
Ending balance, outstanding	525,094	664,785	695,488
Options exercisable at year end	342,048	395,986	300,632
Weighted-average exercise price [Abstract]
Outstanding at beginning of year (in dollars per share)	$ 138.78	$ 133.37	$ 125.96
Granted (in dollars per share)	227.75	176.65	153.54
Assumed - Merger (in dollars per share)	0.00	121.03	0.00
Exercised (in dollars per share)	131.53	113.72	102.43
Forfeited and canceled (in dollars per share)	136.11	144.29	135.25
Outstanding at end of year (in dollars per share)	154.98	138.78	133.37
Options exercisable at year end (in dollars per share)	$ 152.42	$ 133.99	$ 119.09