Stock Compensation - ESPP (Details) - Employee stock purchase plan	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, Beginning balance (in shares) | shares	202,179
Granted (in shares) | shares	847,535
Exercised (in shares) | shares	(819,878)
Options outstanding, Ending balance (in shares) | shares	229,836
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, Outstanding, Beginning of period (in dollars per share) | $ / shares	$ 89.74
Weighted-average exercise price, Granted (in dollars per share) | $ / shares	87.48
Weighted-average exercise price, Exercised (in dollars per share) | $ / shares	90.06
Weighted-average exercise price, Outstanding, End of period (in dollars per share) | $ / shares	$ 80.29