Supplemental Quarterly Financial Data (Unaudited) (Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Data
Net sales	$ 719,359	$ 588,117	$ 548,249	$ 470,148	$ 606,788	$ 548,622	$ 500,381	$ 442,894	$ 2,325,873	$ 2,098,685	$ 2,023,078
Gross margin	175,696	160,220	146,918	123,364	171,659	153,872	133,282	113,746
Earnings before income taxes	79,027	54,417	48,647	37,487	86,765	68,687	50,236	47,059	219,578	252,747	226,486
Net Earnings:
Net earnings	$ 74,512	$ 49,117	$ 38,489	$ 18,260	$ 62,228	$ 53,626	$ 38,105	$ 46,548	$ 180,378	$ 200,507	$ 180,838
Earnings per share:
Basic earnings per share	$ 1.21	$ 0.80	$ 0.63	$ 0.30	$ 1.02	$ 0.87	$ 0.62	$ 0.76	$ 2.93	$ 3.27	$ 2.92
Diluted earnings per share	1.16	0.77	0.60	0.29	0.98	0.85	0.60	0.73	2.82	3.16	2.85
Cash dividends per share	$ 0.1425	$ 0.1425	$ 0.1425	$ 0.1250	$ 0.1250	$ 0.1250	$ 0.1250	$ 0.1100	$ 0.5525	$ 0.4850	$ 0.4300