Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income (loss)	$ (494,497)	$ (33,656)	$ 482,672
Adjustment for (income) loss from discontinued operations	(1,895)	1,146	10,338
Income (loss) from continuing operations	(496,392)	(32,510)	493,010
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	481,885	562,803	583,802
Asset impairment charges	563,234	224,327	23,128
Amortization of debt discount and debt issuance costs	1,817	1,732	1,067
Provision for bad debt	2,203	2,321	2,193
Stock-based compensation	36,329	34,292	31,687
Loss (gain) on investment securities	8,720	54,488	(1)
Gain on sale of assets	(46,775)	(39,691)	(22,660)
Gain on sale of subsidiary	(14,963)	0	0
Deferred income tax benefit	(157,555)	(44,554)	(486,758)
Other	(200)	(3,295)	7,623
Change in assets and liabilities:
Accounts receivable	300,807	70,323	(85,202)
Inventories of materials and supplies	7,197	1,821	(22,427)
Prepaid expenses and other	(5,506)	(176)	(3,827)
Other noncurrent assets	2,820	(10,430)	5,568
Accounts payable	(9,414)	(9,147)	(4,461)
Accrued liabilities	(138,414)	40,887	43,798
Deferred income tax liability	908	371	2,268
Other noncurrent liabilities	2,227	2,251	(10,787)
Net cash provided by operating activities from continuing operations	538,928	855,813	558,021
Net cash used in operating activities from discontinued operations	(47)	(62)	(169)
Net cash provided by operating activities	538,881	855,751	557,852
Cash flows from investing activities:
Capital expenditures	(140,795)	(458,402)	(466,584)
Purchase of short-term investments	(134,641)	(97,652)	(71,049)
Payment for acquisition of business, net of cash acquired	0	(16,163)	(47,886)
Proceeds from sale of short-term investments	94,646	86,765	68,776
Proceeds from sale of subsidiary	15,056	0	0
Proceeds from sale of marketable securities	0	11,999	0
Proceeds from asset sales	78,399	50,817	44,381
Other	(550)	0	0
Net cash used in investing activities	(87,885)	(422,636)	(472,362)
Cash flows from financing activities:
Dividends paid	(260,335)	(313,421)	(308,430)
Debt issuance costs	0	(3,912)	0
Proceeds from stock option exercises	4,100	3,053	6,355
Payments for employee taxes on net settlement of equity awards	(3,784)	(6,418)	(7,114)
Payment of contingent consideration from acquisition of business	(8,250)	0	(10,625)
Payments for early extinguishment of long-term debt	0	(12,852)	0
Share repurchases	(28,505)	(42,779)	0
Other	(446)	0	0
Net cash used in financing activities	(297,220)	(376,329)	(319,814)
Net increase (decrease) in cash and cash equivalents and restricted cash	153,776	56,786	(234,324)
Cash and cash equivalents and restricted cash, beginning of period	382,971	326,185	560,509
Cash and cash equivalents and restricted cash, end of period	536,747	382,971	326,185
Cash paid during the period:
Interest paid	22,928	26,739	20,502
Income tax paid (refund), net	46,700	16,218	(38,400)
Payments for operating leases	18,646
Changes in accounts payable and accrued liabilities related to purchases of property, plant and equipment	$ 3,123	$ 17,771	$ (2,245)