Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		76 Months Ended
	May 08, 2017	Mar. 31, 2017	Mar. 31, 2016	May 08, 2017
Earnings Per Share
Common stock repurchased, shares		1,829	1,231
Common stock repurchased, average price per share		$ 268.09	$ 254.02
Common stock repurchased, value		$ 490,312	$ 312,637
Subsequent event [Member]
Earnings Per Share
Common stock repurchased, shares	600			59,400
Common stock repurchased, average price per share	$ 254.61			$ 126.40
Common stock repurchased, value	$ 152,200			$ 7,500,000