CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net (loss) income	$ (19,191)	$ 161,518
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation	83,251	83,880
Amortization	3,367	1,607
Provision for doubtful accounts	2,369	1,141
Deferred income tax benefit	(525)	(650)
Share-based compensation expense	7,566	5,009
Asset impairment	58,962	65,432
(Gain) loss on sale of assets	(118)	77
(Gain) on extinguishment of debt	0	(8,397)
Other, net	0	(1,137)
Changes in assets and liabilities:
Accounts receivable	38,217	62,963
Income tax receivable	3,206	507
Inventories of materials and supplies	(168)	16,187
Prepaid expenses, deferred costs and other current assets	6,072	14,709
Deferred costs and other assets	(4,201)	(1,381)
Accounts payable	3,425	(25,306)
Accrued liabilities	4,023	(3,760)
Income tax payable	288	6,534
Deferred credits and other liabilities	6,720	1,220
Net cash provided by operating activities	193,263	380,153
Cash flows from investing activities:
Capital expenditures	(154,448)	(176,175)
Proceeds from sale of assets	0	6,681
Net cash used in investing activities	(154,448)	(169,494)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	125,000	45,000
Principal payments on long-term debt	(55,000)	(120,156)
Dividends paid	0	(21,746)
Payments related to exercise of stock options	0	(928)
Proceeds from issuance of common stock	180,966	0
Net cash provided by (used in) financing activities	250,966	(97,830)
Net increase in cash and cash equivalents	289,781	112,829
Cash and cash equivalents, at beginning of period	145,427	113,983
Cash and cash equivalents, at end of period	435,208	226,812
Non-cash activities:
(Decrease) increase in accounts payable related to capital expenditures	(5,031)	950
Increase in deferred credits not yet collected	$ 9,125	$ 0