Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Revenue	$ 291,591	$ 262,466	$ 202,332	$ 218,418	$ 272,717	$ 243,294	$ 179,725	$ 199,597	$ 974,807	$ 895,333	$ 791,447
Gross profit	85,522	83,531	54,877	64,271	90,301	76,762	47,141	55,687	288,201	269,891	225,693
Net income (loss)	$ 16,873	$ 17,785	$ 2,384	$ 12,721	$ 126,774	$ 23,008	$ (25,198)	$ 7,084	$ 49,763	$ 131,668	$ 16,058
Basic earnings (loss) per share (in dollars per share)	$ 0.21	$ 0.23	$ 0.03	$ 0.17	$ 1.72	$ 0.30	$ (0.34)	$ 0.09	$ 0.65	$ 1.78	$ 0.20
Diluted earnings (loss) per share (in dollars per share)	$ 0.21	$ 0.23	$ 0.03	$ 0.17	$ 1.68	$ 0.30	$ (0.34)	$ 0.09	$ 0.64	$ 1.73	$ 0.20
Income tax benefit (provision)					$ 96,800				$ (22,756)	$ 94,458	$ (3,574)
Valuation allowance utilized in period										12,500
Change in deferred tax valuation allowance									$ 208	$ (109,277)	$ (7,994)
Loss on extinguishment of debt	$ 8,700						$ 24,800