Guarantor and Non-Guarantor Financial Information - Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenue	$ 648,872	$ 498,564	$ 1,790,443	$ 1,272,437
Operating costs and other	642,655	526,592	1,781,959	1,415,301
Operating income (loss) from continuing operations	6,217	(28,028)	8,484	(142,864)
Other (expense) income, net	2,137	789	6,117	3,678
Interest expense	(5,993)	(6,364)	(17,794)	(17,503)
Income (loss) from continuing operations before income taxes	2,361	(33,603)	(3,193)	(156,689)
Income tax provision (benefit)	10,535	(10,478)	(494,028)	(50,537)
(Loss) income from continuing operations	(8,174)	(23,125)	490,835	(106,152)
Income from discontinued operations before income taxes	8,383	3,223	9,127	2,705
Income tax provision	8,217	1,897	19,743	2,233
Income (loss) from discontinued operations	166	1,326	(10,616)	472
Net income (loss)	(8,008)	(21,799)	480,219	(105,680)
Eliminations
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenue	(27)	(18)	(64)	(51)
Operating costs and other	(218)	(216)	(669)	(677)
Operating income (loss) from continuing operations	191	198	605	626
Other (expense) income, net	(191)	(198)	(605)	(626)
Equity in net income (loss) of subsidiaries	6,976	19,595	(497,765)	110,053
Income (loss) from continuing operations before income taxes	6,976	19,595	(497,765)	110,053
(Loss) income from continuing operations	6,976	19,595	(497,765)	110,053
Net income (loss)	6,976	19,595	(497,765)	110,053
Guarantor/Parent | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating costs and other	4,240	3,364	12,627	10,124
Operating income (loss) from continuing operations	(4,240)	(3,364)	(12,627)	(10,124)
Other (expense) income, net	196	(4)	477	(3)
Interest expense	(108)	(87)	(274)	(260)
Equity in net income (loss) of subsidiaries	(4,883)	(19,510)	494,574	(99,179)
Income (loss) from continuing operations before income taxes	(9,035)	(22,965)	482,150	(109,566)
Income tax provision (benefit)	(1,027)	(1,166)	1,931	(3,886)
(Loss) income from continuing operations	(8,008)	(21,799)	480,219	(105,680)
Net income (loss)	(8,008)	(21,799)	480,219	(105,680)
Issuer Subsidiary | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenue	574,252	439,227	1,584,970	1,103,877
Operating costs and other	557,994	463,220	1,542,815	1,218,266
Operating income (loss) from continuing operations	16,258	(23,993)	42,155	(114,389)
Other (expense) income, net	1,854	2,052	5,226	4,885
Interest expense	(5,117)	(5,294)	(15,368)	(15,151)
Equity in net income (loss) of subsidiaries	(2,093)	(85)	3,191	(10,874)
Income (loss) from continuing operations before income taxes	10,902	(27,320)	35,204	(135,529)
Income tax provision (benefit)	17,384	(7,360)	(459,571)	(37,320)
(Loss) income from continuing operations	(6,482)	(19,960)	494,775	(98,209)
Net income (loss)	(6,482)	(19,960)	494,775	(98,209)
Non-Guarantor Subsidiaries | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS
Operating revenue	74,647	59,355	205,537	168,611
Operating costs and other	80,639	60,224	227,186	187,588
Operating income (loss) from continuing operations	(5,992)	(869)	(21,649)	(18,977)
Other (expense) income, net	278	(1,061)	1,019	(578)
Interest expense	(768)	(983)	(2,152)	(2,092)
Income (loss) from continuing operations before income taxes	(6,482)	(2,913)	(22,782)	(21,647)
Income tax provision (benefit)	(5,822)	(1,952)	(36,388)	(9,331)
(Loss) income from continuing operations	(660)	(961)	13,606	(12,316)
Income from discontinued operations before income taxes	8,383	3,223	9,127	2,705
Income tax provision	8,217	1,897	19,743	2,233
Income (loss) from discontinued operations	166	1,326	(10,616)	472
Net income (loss)	$ (494)	$ 365	$ 2,990	$ (11,844)