Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		100 Months Ended
	May 06, 2019	Mar. 31, 2019	Mar. 31, 2018	May 06, 2019
Earnings Per Share
Common stock repurchased, shares		927	2,188
Common stock repurchased, average price per share		$ 347.09	$ 251.08
Common stock repurchased, value		$ 321,846	$ 549,428
Subsequent event [Member]
Earnings Per Share
Common stock repurchased, shares	100			73,400
Common stock repurchased, average price per share	$ 377.59			$ 151.58
Common stock repurchased, value	$ 52,100			$ 11,100,000