Summarized Data for Each of the Quarters (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 26,285	$ 40,728	$ 68,551	$ 101,348	$ 68,288	$ 78,148	$ 76,420	$ 77,751	$ 236,912	$ 300,607	$ 191,664
Gross profit	6,089	15,376	27,903	47,091	29,780	33,875	35,561	40,545	96,459	139,761	82,064
Income (loss) from operations	(3,282)	5,458	15,956	35,667	19,132	24,991	25,556	31,548	53,799	101,227	50,865
Other income (expense), net	10	(129)	11	(148)	274	(50)	(532)	174	(256)	(134)	997
Net income	$ (1,833)	$ 3,752	$ 10,816	$ 24,176	$ 13,684	$ 16,991	$ 16,869	$ 22,013	$ 36,911	$ 69,557	$ 35,118
Basic earnings per share	$ (0.14)	$ 0.29	$ 0.83	$ 1.86	$ 1.06	$ 1.32	$ 1.31	$ 1.72	$ 2.82	$ 5.40	$ 2.76
Diluted earnings per share	$ (0.14)	$ 0.29	$ 0.82	$ 1.85	$ 1.05	$ 1.31	$ 1.30	$ 1.70	$ 2.81	$ 5.38	$ 2.74