Quarterly Financial Information (Unaudited) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Quarterly Financial Information (Unaudited)
Net sales	$ 236,658	$ 199,766	$ 193,949	$ 182,597	$ 231,086	$ 192,223	$ 174,778	$ 173,495	$ 812,970	$ 771,582	$ 685,740
Net earnings	$ 24,858	$ 20,067	$ 18,797	$ 17,317	$ 28,452	$ 19,019	$ 9,994	$ 34,671	$ 81,039	$ 92,136	$ 53,703
Earnings per share:
Basic	$ 0.96	$ 0.77	$ 0.73	$ 0.67	$ 1.10	$ 0.73	$ 0.39	$ 1.34	$ 3.12	$ 3.56	$ 2.08
Diluted	0.95	0.77	0.72	0.66	1.09	0.73	0.38	1.33	3.10	3.54	2.07
Dividends declared per common share	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.08	$ 0.32	$ 0.32	$ 0.32
Common Stock per share:
High	85.86	82.70	71.29	71.47	70.20	60.25	66.80	65.95
Low	$ 73.04	$ 67.43	$ 62.91	$ 59.00	$ 57.00	$ 54.35	$ 57.15	$ 51.55