Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Net sales	$ 964,230	$ 967,890	$ 937,755	$ 964,468	$ 944,288	$ 949,275	$ 919,471	$ 940,464	$ 3,834,343	$ 3,753,498	$ 3,622,216
Gross profit	475,311	481,319	467,452	473,769	467,540	475,711	456,395	460,526	1,897,851	1,860,172	1,795,263
Net earnings	$ 56,180	$ 62,463	$ 61,535	$ 54,909	$ 61,750	$ 67,756	$ 58,492	$ 57,995	$ 235,087	$ 245,993	$ 261,151
Earnings per common share
Basic (in dollars per share)	$ 0.36	$ 0.40	$ 0.39	$ 0.35	$ 0.40	$ 0.43	$ 0.36	$ 0.35	$ 1.50	$ 1.54	$ 1.52
Diluted (in dollars per share)	$ 0.36	$ 0.39	$ 0.39	$ 0.35	$ 0.39	$ 0.42	$ 0.35	$ 0.35	$ 1.49	$ 1.51	$ 1.48