Quarterly Financial Information (Unaudited) (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
Net sales	$ 207,005	$ 171,189	$ 161,178	$ 146,368	$ 159,505	$ 140,191	$ 138,930	$ 132,833	$ 685,740	$ 571,459	$ 537,291
Net earnings	$ 19,174	$ 12,645	$ 11,157	$ 10,727	$ 16,915	$ 11,528	$ 8,610	$ 8,829	$ 53,703	$ 45,882	$ 42,512
Basic earnings (loss) per share:
Net earnings	$ 0.74	$ 0.49	$ 0.43	$ 0.42	$ 0.66	$ 0.45	$ 0.33	$ 0.34	$ 2.08	$ 1.78	$ 1.63
Diluted earnings (loss) per share:
Net earnings	0.74	0.49	0.43	0.41	0.65	0.44	0.33	0.34	2.07	1.77	1.62
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

Aggregate dividends declared during the period for each share of common stock outstanding.

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