SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Segment information
Sales	$ 985,038	$ 952,087	$ 893,430	$ 889,152	$ 864,536	$ 840,197	$ 838,309	$ 844,572	$ 3,719,707	$ 3,387,614	$ 3,151,802
Segment Operating Income (Loss)									1,122,913	1,021,648	960,285
Depreciation									523,549	455,623	387,549
Total assets	6,714,655				6,261,122				6,714,655	6,261,122	5,713,466
Additions to Long-Lived Assets									1,047,176	791,741	1,082,678
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									1,122,913	1,021,648	960,285
Income from asset sales									19,585	18,923	19,223
Corporate general and administrative costs and corporate depreciation									(87,711)	(83,910)	(69,909)
Operating income from continuing operations	263,502	271,912	255,342	264,031	243,234	239,960	232,920	240,547	1,054,787	956,661	909,599
Other income (expense):
Interest and dividend income									1,583	1,653	1,380
Interest expense									(4,654)	(6,129)	(8,653)
Gain on sale of investment securities									45,234	162,121
Other									(636)	(9)	254
Total other income (expense)									41,527	157,636	(7,019)
Income from continuing operations before income taxes									1,096,314	1,114,297	902,580
Other
Segment information
Sales									13,410	13,461	14,214
Segment Operating Income (Loss)									(9,068)	(8,602)	(8,824)
Depreciation									15,383	14,785	10,670
Total assets	726,776				881,436				726,776	881,436	663,496
Additions to Long-Lived Assets									27,117	9,872	29,301
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									(9,068)	(8,602)	(8,824)
Operating segment
Segment information
Sales									3,720,574	3,388,472	3,152,643
Operating segment | Other
Segment information
Sales									14,277	14,319	15,055
Inter-Segment
Segment information
Sales									(867)	(858)	(841)
Inter-Segment | Other
Segment information
Sales									867	858	841
Contract Drilling:
Segment information
Sales									3,706,297	3,374,153	3,137,588
Segment Operating Income (Loss)									1,131,981	1,030,250	969,109
Depreciation									508,166	440,838	376,879
Total assets	5,987,879				5,379,686				5,987,879	5,379,686	5,049,970
Additions to Long-Lived Assets									1,020,059	781,869	1,053,377
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									1,131,981	1,030,250	969,109
Contract Drilling: | U.S. Land
Segment information
Sales									3,099,954	2,785,449	2,678,475
Segment Operating Income (Loss)									1,025,745	932,591	906,968
Depreciation									455,934	391,072	332,723
Total assets	5,260,810				4,743,644				5,260,810	4,743,644	4,422,297
Additions to Long-Lived Assets									930,263	726,206	991,966
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									1,025,745	932,591	906,968
Contract Drilling: | Offshore
Segment information
Sales									250,811	221,863	189,086
Segment Operating Income (Loss)									69,819	53,064	41,775
Depreciation									12,300	13,766	13,455
Total assets	137,101				149,128				137,101	149,128	160,135
Additions to Long-Lived Assets									4,372	4,470	8,547
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									69,819	53,064	41,775
Contract Drilling: | International Land
Segment information
Sales									355,532	366,841	270,027
Segment Operating Income (Loss)									36,417	44,595	20,366
Depreciation									39,932	36,000	30,701
Total assets	589,968				486,914				589,968	486,914	467,538
Additions to Long-Lived Assets									85,424	51,193	52,864
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									36,417	44,595	20,366
Contract Drilling: | Operating segment
Segment information
Sales									3,706,297	3,374,153	3,137,588
Contract Drilling: | Operating segment | U.S. Land
Segment information
Sales									3,099,954	2,785,449	2,678,475
Contract Drilling: | Operating segment | Offshore
Segment information
Sales									250,811	221,863	189,086
Contract Drilling: | Operating segment | International Land
Segment information
Sales									$ 355,532	$ 366,841	$ 270,027