Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 161,518	$ 168,887
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	83,880	87,103
Amortization	1,607	3,761
Provision for doubtful accounts	1,141	160
Deferred income tax benefit	(650)	(3,512)
Share-based compensation expense	5,009	8,119
Asset impairment	65,432	60,777
Loss on sale of assets	77	15,335
(Gain) on extinguishment of debt	(8,397)	0
Other, net	(1,137)	0
Changes in assets and liabilities:
Accounts receivable	62,963	15,829
Income tax receivable	507	(3,604)
Inventories of materials and supplies	16,187	(17,110)
Prepaid expenses, deferred costs and other current assets	14,709	9,789
Deferred costs and other assets	(1,381)	(357)
Accounts payable	(25,306)	2,825
Accrued liabilities	(3,760)	(3,691)
Income tax payable	6,534	(310)
Deferred credits and other liabilities	1,220	5,747
Net cash provided by operating activities	380,153	349,748
Cash flows from investing activities:
Capital expenditures	(176,175)	(177,130)
Proceeds from sale of assets	6,681	2,524
Net cash used in investing activities	(169,494)	(174,606)
Cash flows from financing activities:
Proceeds from borrowing of long-term debt	45,000	0
Principal repayments on long-term debt	(120,156)	(135,000)
Repayments on short-term debt, net	0	(11,885)
Dividends paid	(21,746)	(16,163)
Proceeds (payments) related to exercise of stock options	(928)	1,186
Debt issuance costs paid	0	(3,126)
Net cash used by financing activities	(97,830)	(164,988)
Net increase in cash and cash equivalents	112,829	10,154
Cash and cash equivalents, at beginning of period	113,983	80,080
Cash and cash equivalents, at end of period	226,812	90,234
Non-cash activities:
Increase (decrease) in accounts payable and accrued liabilities related to capital expenditures	$ 950	$ 3,020