Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Net sales	$ 944,288	$ 949,275	$ 919,471	$ 940,464	$ 906,435	$ 912,101	$ 898,239	$ 905,441	$ 3,753,498	$ 3,622,216	$ 3,523,644
Gross profit	467,540	475,711	456,396	460,526	449,358	457,083	444,454	444,368	1,860,172	1,795,263	1,743,259
Net earnings	$ 61,750	$ 67,756	$ 58,492	$ 57,995	$ 64,812	$ 72,466	$ 64,889	$ 58,983	$ 245,993	$ 261,151	$ 233,064
Earnings per common share
Basic (in dollars per share)	$ 0.40	$ 0.43	$ 0.36	$ 0.35	$ 0.39	$ 0.43	$ 0.37	$ 0.33	$ 1.54	$ 1.52	$ 1.27
Diluted (in dollars per share)	$ 0.39	$ 0.42	$ 0.35	$ 0.35	$ 0.38	$ 0.42	$ 0.36	$ 0.32	$ 1.51	$ 1.48	$ 1.24