Supplemental Quarterly Financial Data (Unaudited) (Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Quarterly Financial Data
Net sales	$ 606,788	$ 548,622	$ 500,381	$ 442,894	$ 590,922	$ 507,664	$ 479,382	$ 445,110	$ 2,098,685	$ 2,023,078	$ 2,038,303
Gross margin	171,659	153,872	133,282	113,746	163,659	134,825	131,081	109,553
Earnings before income taxes	86,765	68,687	50,236	47,059	80,756	63,408	54,366	27,956	252,747	226,486	240,949
Net Earnings:
Net earnings	$ 62,228	$ 53,626	$ 38,105	$ 46,548	$ 63,147	$ 51,047	$ 40,824	$ 25,820	$ 200,507	$ 180,838	$ 181,452
Earnings per share:
Basic earnings per share	$ 1.02	$ 0.87	$ 0.62	$ 0.76	$ 1.03	$ 0.83	$ 0.66	$ 0.41	$ 3.27	$ 2.92	$ 2.81
Diluted earnings per share	0.98	0.85	0.60	0.73	0.99	0.81	0.65	0.40	3.16	2.85	2.75
Cash dividends per share	$ 0.125	$ 0.125	$ 0.125	$ 0.110	$ 0.110	$ 0.110	$ 0.110	$ 0.100	$ 0.485	$ 0.430	$ 0.380