GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
CONDENSED CONSOLIDATING STATEMENTS OF CASH FLOWS
Net cash provided by (used in) operating activities	$ 753,597	$ 1,428,574	$ 1,129,082
INVESTING ACTIVITIES:
Capital expenditures	(257,169)	(1,131,445)	(951,536)
Purchase of short-term investments	(57,276)	(45,607)
Proceeds from sale of short-term investments	58,381
Proceeds from asset sales	21,845	22,643	30,176
Proceeds from sale of investments			49,205
Net cash used in investing activities	(234,219)	(1,154,409)	(872,155)
FINANCING ACTIVITIES:
Payments on long-term debt	(40,000)	(40,000)	(115,000)
Proceeds from senior notes, net of discount		497,125
Debt issuance costs	(1,111)	(5,474)
Proceeds on short-term debt		1,002
Payments on short-term debt		(1,002)
Repurchase of common stock		(59,654)
Dividends paid	(300,152)	(298,367)	(264,386)
Exercise of stock options, net of tax withholding	1,040	2,650	23,250
Tax withholdings related to net share settlements of restricted stock	(3,912)	(5,140)	(3,049)
Excess tax benefit from stock-based compensation	934	3,772	26,616
Net cash provided by (used in) financing activities	(343,201)	94,912	(332,569)
Net increase (decrease) in cash and cash equivalents	176,177	369,077	(75,642)
Cash and cash equivalents, beginning of period	729,384	360,307	435,949
Cash and cash equivalents, end of period	905,561	729,384	360,307
Guarantor/Parent | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF CASH FLOWS
Net cash provided by (used in) operating activities	3,521	3,623	(21,094)
INVESTING ACTIVITIES:
Capital expenditures	(16,119)	(24,818)	(17,786)
Intercompany transfers	16,119	24,818	17,786
Proceeds from asset sales	9	1	2
Net cash used in investing activities	9	1	2
FINANCING ACTIVITIES:
Repurchase of common stock		(59,654)
Intercompany transfers	300,152	358,021	264,386
Dividends paid	(300,152)	(298,367)	(264,386)
Exercise of stock options, net of tax withholding	1,040	2,650	23,250
Tax withholdings related to net share settlements of restricted stock	(3,912)	(5,140)	(3,049)
Excess tax benefit from stock-based compensation	(775)	78	(957)
Net cash provided by (used in) financing activities	(3,647)	(2,412)	19,244
Net increase (decrease) in cash and cash equivalents	(117)	1,212	(1,848)
Cash and cash equivalents, beginning of period	(838)	(2,050)	(202)
Cash and cash equivalents, end of period	(955)	(838)	(2,050)
Issuer Subsidiary | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF CASH FLOWS
Net cash provided by (used in) operating activities	776,364	1,379,707	1,050,609
INVESTING ACTIVITIES:
Capital expenditures	(235,078)	(1,064,288)	(840,341)
Purchase of short-term investments	(57,276)	(45,607)
Proceeds from sale of short-term investments	58,381
Intercompany transfers	(16,119)	(24,818)	(17,786)
Proceeds from asset sales	19,237	21,329	27,401
Proceeds from sale of investments			49,205
Net cash used in investing activities	(230,855)	(1,113,384)	(781,521)
FINANCING ACTIVITIES:
Payments on long-term debt	(40,000)	(40,000)	(115,000)
Proceeds from senior notes, net of discount		497,125
Debt issuance costs	(1,111)	(5,474)
Intercompany transfers	(300,152)	(358,021)	(264,386)
Excess tax benefit from stock-based compensation	1,509	3,665	27,357
Net cash provided by (used in) financing activities	(339,754)	97,295	(352,029)
Net increase (decrease) in cash and cash equivalents	205,755	363,618	(82,941)
Cash and cash equivalents, beginning of period	693,273	329,655	412,596
Cash and cash equivalents, end of period	899,028	693,273	329,655
Non-Guarantor Subsidiaries | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF CASH FLOWS
Net cash provided by (used in) operating activities	(26,288)	45,244	99,567
INVESTING ACTIVITIES:
Capital expenditures	(5,972)	(42,339)	(93,409)
Proceeds from asset sales	2,599	1,313	2,773
Net cash used in investing activities	(3,373)	(41,026)	(90,636)
FINANCING ACTIVITIES:
Proceeds on short-term debt		1,002
Payments on short-term debt		(1,002)
Excess tax benefit from stock-based compensation	200	29	216
Net cash provided by (used in) financing activities	200	29	216
Net increase (decrease) in cash and cash equivalents	(29,461)	4,247	9,147
Cash and cash equivalents, beginning of period	36,949	32,702	23,555
Cash and cash equivalents, end of period	$ 7,488	$ 36,949	$ 32,702