GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION (Details 4) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
CURRENT ASSETS:
Cash and cash equivalents	$ 717,977	$ 360,909	$ 447,868	$ 96,095
Short-term investments	45,543
Accounts receivable, net of reserve	449,344	705,214
Inventories	128,729	106,241
Deferred income taxes	17,200	16,519
Prepaid expenses and other	72,117	80,912
Current assets of discontinued operations	8,097	7,206
Total current assets	1,439,007	1,277,001
Investments	104,354	236,644
Property, plant and equipment, net	5,567,235	5,188,544	4,676,103
Other assets	41,416	18,809
TOTAL ASSETS	7,152,012	6,720,998
CURRENT LIABILITIES:
Accounts payable	110,704	182,031
Accrued liabilities	198,053	282,278
Long-term debt due within one year	39,094	39,635
Current liabilities of discontinued operations	3,377	3,217
Total current liabilities	351,228	507,161
NONCURRENT LIABILITIES:
Long-term debt	492,443	39,502
Deferred income taxes	1,295,065	1,215,259
Other	111,104	64,110
Noncurrent liabilities of discontinued operations	4,720	3,989
Total noncurrent liabilities	1,903,332	1,322,860
SHAREHOLDERS' EQUITY:
Common stock	11,099	11,051
Additional paid-in capital	420,141	383,972
Retained earnings	4,649,952	4,525,797
Accumulated other comprehensive income (loss)	(1,377)	83,126
Treasury stock, at cost	(182,363)	(112,969)
Total shareholders' equity	4,897,452	4,890,977	4,443,727	3,834,998
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	7,152,012	6,720,998
Eliminations
CURRENT ASSETS:
Cash and cash equivalents	(8,554)	(3,628)	1,556	(1,005)
Accounts receivable, net of reserve	(5,675)	(16,942)
Inventories		1,770
Deferred income taxes	(4,788)	(8,352)
Prepaid expenses and other	(2,714)	54
Total current assets	(21,731)	(27,098)
Intercompany	(1,438,135)	(994,122)
Other assets	(8,153)	(6,621)
Investment in subsidiaries	(5,853,270)	(5,512,105)
TOTAL ASSETS	(7,321,289)	(6,539,946)
CURRENT LIABILITIES:
Accounts payable	(5)	(7)
Accrued liabilities	(10,784)	(6,138)
Total current liabilities	(10,789)	(6,145)
NONCURRENT LIABILITIES:
Deferred income taxes	(12,941)	(14,573)
Intercompany	(1,444,289)	(1,007,123)
Total noncurrent liabilities	(1,457,230)	(1,021,696)
SHAREHOLDERS' EQUITY:
Common stock	(100)	(100)
Additional paid-in capital	(46,173)	(42,835)
Retained earnings	(5,803,141)	(5,381,476)
Accumulated other comprehensive income (loss)	(3,856)	(87,694)
Total shareholders' equity	(5,853,270)	(5,512,105)
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	(7,321,289)	(6,539,946)
Guarantor/Parent | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents	(838)	(2,050)	(202)	(1,080)
Accounts receivable, net of reserve	152	(31)
Deferred income taxes	2,834	5,372
Prepaid expenses and other	20,018	8,863
Total current assets	22,166	12,154
Investments	12,871	14,344
Property, plant and equipment, net	55,902	42,027
Intercompany	15,875	14,855
Other assets	8,387	8,110
Investment in subsidiaries	5,625,360	5,276,750
TOTAL ASSETS	5,740,561	5,368,240
CURRENT LIABILITIES:
Accounts payable	80,673	80,562
Accrued liabilities	10,688	31,960
Total current liabilities	91,361	112,522
NONCURRENT LIABILITIES:
Intercompany	733,008	346,545
Other	18,740	18,196
Total noncurrent liabilities	751,748	364,741
SHAREHOLDERS' EQUITY:
Common stock	11,099	11,051
Additional paid-in capital	420,141	383,972
Retained earnings	4,649,952	4,525,797
Accumulated other comprehensive income (loss)	(1,377)	83,126
Treasury stock, at cost	(182,363)	(112,969)
Total shareholders' equity	4,897,452	4,890,977
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	5,740,561	5,368,240
Issuer Subsidiary | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents	693,273	329,655	412,596	67,074
Short-term investments	45,543
Accounts receivable, net of reserve	374,383	623,274
Inventories	88,010	67,113
Deferred income taxes	19,154	19,499
Prepaid expenses and other	6,713	15,013
Total current assets	1,227,076	1,054,554
Investments	91,483	222,300
Property, plant and equipment, net	5,063,705	4,681,294
Intercompany	1,192,634	782,626
Other assets	1,389	1,197
Investment in subsidiaries	227,910	235,355
TOTAL ASSETS	7,804,197	6,977,326
CURRENT LIABILITIES:
Accounts payable	20,404	80,488
Accrued liabilities	151,607	212,896
Long-term debt due within one year	39,094	39,635
Total current liabilities	211,105	333,019
NONCURRENT LIABILITIES:
Long-term debt	492,443	39,502
Deferred income taxes	1,275,427	1,182,192
Intercompany	185,493	141,066
Other	31,560	19,948
Total noncurrent liabilities	1,984,923	1,382,708
SHAREHOLDERS' EQUITY:
Common stock	100	100
Additional paid-in capital	45,824	42,516
Retained earnings	5,558,389	5,131,289
Accumulated other comprehensive income (loss)	3,856	87,694
Total shareholders' equity	5,608,169	5,261,599
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	7,804,197	6,977,326
Non-Guarantor Subsidiaries | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents	34,096	36,932	$ 33,918	$ 31,106
Accounts receivable, net of reserve	80,484	98,913
Inventories	40,719	37,358
Prepaid expenses and other	48,100	56,982
Current assets of discontinued operations	8,097	7,206
Total current assets	211,496	237,391
Property, plant and equipment, net	447,628	465,223
Intercompany	229,626	196,641
Other assets	39,793	16,123
TOTAL ASSETS	928,543	915,378
CURRENT LIABILITIES:
Accounts payable	9,632	20,988
Accrued liabilities	46,542	43,560
Current liabilities of discontinued operations	3,377	3,217
Total current liabilities	59,551	67,765
NONCURRENT LIABILITIES:
Deferred income taxes	32,579	47,640
Intercompany	525,788	519,512
Other	60,804	25,966
Noncurrent liabilities of discontinued operations	4,720	3,989
Total noncurrent liabilities	623,891	597,107
SHAREHOLDERS' EQUITY:
Additional paid-in capital	349	319
Retained earnings	244,752	250,187
Total shareholders' equity	245,101	250,506
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 928,543	$ 915,378