CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net (loss) income	$ (23,541)	$ 261,023
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation	121,751	124,964
Amortization	4,357	2,407
Provision for doubtful accounts	2,472	4,619
Deferred income tax benefit	86	(378)
Share-based compensation expense	10,657	8,224
Asset impairment	59,173	64,753
Loss (gain) on sale of assets	261	(71)
Gain on extinguishment of debt	0	(58,863)
Other, net	0	(1,137)
Changes in assets and liabilities:
Accounts receivable	32,479	121,964
Income tax receivable	3,326	511
Inventories of materials and supplies	(891)	12,988
Prepaid expenses, deferred costs and other current assets	6,324	19,377
Deferred costs and other assets	(6,440)	(1,019)
Accounts payable	911	(33,674)
Accrued liabilities	10,400	(3,274)
Income tax payable	(1,055)	(376)
Deferred credits and other liabilities	28,558	(6,623)
Net cash provided by operating activities	248,828	515,415
Cash flows from investing activities:
Capital expenditures	(173,246)	(198,248)
Proceeds from sale of assets	2,338	20,813
Net cash used in investing activities	(170,908)	(177,435)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	125,000	45,000
Principal payments on long-term debt	(55,000)	(290,110)
Dividends paid	0	(21,746)
Payments related to exercise of stock options	0	(930)
Proceeds from issuance of common stock	180,966	0
Windfall tax benefits from share-based payment arrangements	0	14,797
Net cash provided by (used in) financing activities	250,966	(252,989)
Net increase in cash and cash equivalents	328,886	84,991
Cash and cash equivalents, at beginning of period	145,427	113,983
Cash and cash equivalents, at end of period	474,313	198,974
Non-cash activities:
Increase in accounts payable related to capital expenditures	$ 9,612	$ 7,902