Quarterly 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 Information Disclosure [Abstract]
Revenues	$ 134,897	$ 122,130	$ 101,505	$ 90,184	$ 94,963	$ 85,927	$ 104,680	$ 110,341	$ 448,716	$ 395,911	$ 565,243
Gross profit	24,005	18,375	12,421	10,554	10,894	9,054	15,822	14,999	65,355	50,769	106,205
Net income (loss)	$ 1,539	$ 301	$ (3,330)	$ (5,662)	$ (5,142)	$ (3,215)	$ (829)	$ (300)	$ (7,152)	$ (9,486)	$ 15,510
Earnings (loss) per share:
Basic (in dollars per share)	$ 0.13	$ 0.03	$ (0.29)	$ (0.49)	$ (0.45)	$ (0.28)	$ (0.07)	$ (0.03)	$ (0.62)	$ (0.83)	$ 1.36
Diluted (in dollars per share)	$ 0.13	$ 0.03	$ (0.29)	$ (0.49)	$ (0.45)	$ (0.28)	$ (0.07)	$ (0.03)	$ (0.62)	$ (0.83)	$ 1.36