SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Segment information
Sales	$ 864,536	$ 840,197	$ 838,309	$ 844,572	$ 829,447	$ 819,785	$ 769,982	$ 732,588	$ 3,387,614	$ 3,151,802	$ 2,543,894
Segment Operating Income (Loss)									1,021,648	960,285	748,935
Depreciation									455,623	387,549	315,468
Total assets	6,261,122				5,713,466				6,261,122	5,713,466	4,996,362
Additions to Long-Lived Assets									791,741	1,082,678	730,347
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									1,021,648	960,285	748,935
Income from asset sales									18,923	19,223	13,903
Corporate general and administrative costs and corporate depreciation									(83,910)	(69,909)	(60,327)
Operating income from continuing operations	243,234	239,960	232,920	240,547	239,380	232,655	207,025	230,539	956,661	909,599	702,511
Other income (expense):
Interest and dividend income									1,653	1,380	1,951
Interest expense									(6,129)	(8,653)	(17,355)
Gain on sale of investment securities		92,400		5,500					162,121		913
Other									(9)	254	(953)
Total other income (expense)									157,636	(7,019)	(15,444)
Income from continuing operations before income taxes									1,114,297	902,580	687,067
Other
Segment information
Sales									13,461	14,214	15,120
Segment Operating Income (Loss)									(8,602)	(8,824)	(7,682)
Depreciation									14,785	10,670	8,639
Total assets	881,436				663,496				881,436	663,496	792,177
Additions to Long-Lived Assets									9,872	29,301	8,368
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									(8,602)	(8,824)	(7,682)
Operating segment
Segment information
Sales									3,388,472	3,152,643	2,544,723
Operating segment | Other
Segment information
Sales									14,319	15,055	15,949
Inter-segment
Segment information
Sales									(858)	(841)	(829)
Inter-segment | Other
Segment information
Sales									(858)	(841)	(829)
Contract Drilling
Segment information
Sales									3,374,153	3,137,588	2,528,774
Segment Operating Income (Loss)									1,030,250	969,109	756,617
Depreciation									440,838	376,879	306,829
Total assets	5,379,686				5,049,970				5,379,686	5,049,970	4,204,185
Additions to Long-Lived Assets									781,869	1,053,377	721,979
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									1,030,250	969,109	756,617
Contract Drilling | U.S. Land
Segment information
Sales									2,785,449	2,678,475	2,100,508
Segment Operating Income (Loss)									932,591	906,968	691,615
Depreciation									391,072	332,723	264,127
Total assets	4,743,644				4,422,297				4,743,644	4,422,297	3,719,387
Additions to Long-Lived Assets									726,206	991,966	694,249
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									932,591	906,968	691,615
Contract Drilling | Offshore
Segment information
Sales									221,863	189,086	201,417
Segment Operating Income (Loss)									53,064	41,775	45,291
Depreciation									13,766	13,455	14,684
Total assets	149,128				160,135				149,128	160,135	151,656
Additions to Long-Lived Assets									4,470	8,547	7,092
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									53,064	41,775	45,291
Contract Drilling | International Land
Segment information
Sales									366,841	270,027	226,849
Segment Operating Income (Loss)									44,595	20,366	19,711
Depreciation									36,000	30,701	28,018
Total assets	486,914				467,538				486,914	467,538	333,142
Additions to Long-Lived Assets									51,193	52,864	20,638
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									44,595	20,366	19,711
Contract Drilling | Operating segment
Segment information
Sales									3,374,153	3,137,588	2,528,774
Contract Drilling | Operating segment | U.S. Land
Segment information
Sales									2,785,449	2,678,475	2,100,508
Contract Drilling | Operating segment | Offshore
Segment information
Sales									221,863	189,086	201,417
Contract Drilling | Operating segment | International Land
Segment information
Sales									$ 366,841	$ 270,027	$ 226,849