Business Segment Information - Segment Operating Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total segment operating income	$ 418,973	$ 399,987
Operating segments
Segment Reporting Information [Line Items]
Total segment operating income	488,050	486,195
Intersegment eliminations
Segment Reporting Information [Line Items]
Total segment operating income	(407)	(13)
Pharmaceutical Distribution Services | Operating segments
Segment Reporting Information [Line Items]
Total segment operating income	388,182	379,060
Other | Operating segments
Segment Reporting Information [Line Items]
Total segment operating income	$ 100,275	$ 107,148