Quarterly Data (unaudited) (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 Data (unaudited)
Net revenues	$ 122,313	$ 113,114	$ 110,206	$ 89,693	$ 100,765	$ 97,977	$ 103,112	$ 93,355	$ 435,326	$ 395,209	$ 406,359
Gross profit	15,946	13,270	11,452	7,010	5,773	3,662	9,788	10,487	47,678	29,710	47,580
Net income (loss)	$ 2,130	$ 713	$ (2,068)	$ (22,526)	$ (3,661)	$ (3,967)	$ (1,890)	$ (672)	$ (21,751)	$ (10,190)	$ 5,020
Net income (loss) per share:
Basic (in dollars per share)	$ 0.17	$ 0.06	$ (0.17)	$ (1.82)	$ (0.30)	$ (0.32)	$ (0.15)	$ (0.06)	$ (1.75)	$ (0.83)	$ 0.40
Diluted (in dollars per share)	$ 0.17	$ 0.06	$ (0.17)	$ (1.82)	$ (0.30)	$ (0.32)	$ (0.15)	$ (0.06)	$ (1.75)	$ (0.83)	$ 0.40