CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Cash flows from operating activities:
Net income	$ 265,272	$ 432,573	$ 340,822
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	165,669	171,947	147,358
Amortization	3,446	6,299	8,634
Provision for doubtful accounts and inventory obsolescence	9,501	4,286	2,826
Deferred income tax benefit	1,632	(2,747)	(1,270)
Share-based compensation expense	11,862	12,828	14,691
Asset impairment	103,539	60,777	0
(Gain) loss on sale of assets	(222)	15,303	(34,139)
(Gain) on extinguishment of debt	(69,041)	0	0
Change in assets and liabilities:
Accounts receivable	176,614	(72,575)	(43,965)
Income tax receivable	2,610	(2,445)	(1,588)
Inventories of materials and supplies	12,385	(19,068)	(17,220)
Prepaid expenses, deferred costs and other current assets	7,498	(3,655)	15,463
Deferred costs and other assets	(608)	5,917	(11,682)
Accounts payable	(36,227)	(11,967)	1,932
Accrued liabilities	(16,298)	1,637	1,647
Income tax payable	(5,612)	(328)	(2,320)
Deferred credits and other liabilities	(7,012)	5,505	21,431
Net cash provided by operating activities	625,008	604,287	442,620
Cash flows from investing activities:
Capital expenditures	(223,731)	(448,019)	(975,731)
Net proceeds from sale of assets	20,792	(4,402)	61,516
Net cash used in investing activities	(202,939)	(452,421)	(914,215)
Cash flows from financing activities:
Proceeds from borrowing of long-term debt	45,000	225,000	700,000
Principal repayments on long-term debt	(426,623)	(280,000)	(220,000)
Repayments on short-term debt, net	0	(11,885)	(13,979)
Dividends paid	(21,745)	(48,562)	0
Proceeds from exercise of stock options	0	1,064	3,688
Debt issuance costs paid	(451)	(3,580)	(6,804)
Windfall tax benefits from share-based payment arrangements	13,194	0	0
Net cash (used in) or provided by financing activities	(390,625)	(117,963)	462,905
Net increase (decrease) in cash and cash equivalents	31,444	33,903	(8,690)
Cash at beginning of period	113,983	80,080	88,770
Cash at end of period	145,427	113,983	80,080
Cash paid during the period for:
Domestic and foreign income taxes	35,653	50,428	55,777
Interest, net of amounts capitalized	67,958	48,209	35,265
Non-cash activities:
Decrease in accounts payables related to capital expenditures	(8,028)	(9,532)	(2,804)
Dividends payable	0	16,164	16,090
Increase in short-term debt related to funding of insurance policies	$ 0	$ 0	$ 17,793