Quarterly Information (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 94,963	$ 85,927	$ 104,680	$ 110,341	$ 129,793	$ 133,207	$ 152,266	$ 149,977	$ 395,911	$ 565,243	$ 661,858
Gross profit	10,894	9,054	15,822	14,999	25,676	27,285	30,094	23,150	50,769	106,205	108,261
Net income (loss)	$ (5,142)	$ (3,215)	$ (829)	$ (300)	$ 5,508	$ 4,894	$ 5,567	$ (459)	$ (9,486)	$ 15,510	$ 9,439
Earnings (loss) per share:
Basic (in dollars per share)	$ (0.45)	$ (0.28)	$ (0.07)	$ (0.03)	$ 0.48	$ 0.43	$ 0.49	$ (0.04)	$ (0.83)	$ 1.36	$ 0.80
Diluted (in dollars per share)	$ (0.45)	$ (0.28)	$ (0.07)	$ (0.03)	$ 0.48	$ 0.43	$ 0.49	$ (0.04)	$ (0.83)	$ 1.36	$ 0.79