SEGMENT INFORMATION - Reportable segment information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Segment information
Sales	$ 331,708	$ 366,486	$ 438,191	$ 487,847	$ 553,800	$ 661,445	$ 885,670	$ 1,060,787	$ 1,624,232	$ 3,161,702	$ 3,715,968
Segment Operating Income (Loss)									68,200	748,373	1,121,791
Depreciation									598,587	608,039	523,984
Total assets	6,831,955				7,139,145				6,831,955	7,139,145	6,718,110
Additions to Long-Lived Assets									241,290	1,033,241	1,045,820
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									68,200	748,373	1,121,791
Income from asset sales									9,896	11,834	19,083
Corporate general and administrative costs and corporate depreciation									(104,062)	(88,244)	(87,700)
Operating income (loss) from continuing operations	(93,001)	$ (13,256)	$ 41,621	$ 38,670	(24,783)	$ 135,049	$ 231,326	$ 330,371	(25,966)	671,963	1,053,174
Other income (expense)
Interest and dividend income									3,166	5,840	1,543
Interest expense									(22,913)	(15,023)	(4,657)
Gain (loss) on investment securities									(25,989)		45,234
Other									(965)	(901)	(636)
Total other income (expense)									(46,701)	(10,084)	41,484
Income (loss) from continuing operations before income taxes									(72,667)	661,879	1,094,658
Other
Segment information
Sales									13,275	14,187	13,410
Segment Operating Income (Loss)									(7,491)	(10,911)	(9,068)
Depreciation									20,753	19,096	15,383
Total assets	1,234,323				1,025,402				1,234,323	1,025,402	726,174
Additions to Long-Lived Assets									20,076	27,518	27,117
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									(7,491)	(10,911)	(9,068)
Operating segment
Segment information
Sales									1,625,087	3,162,582	3,716,835
Operating segment | Other
Segment information
Sales									14,130	15,067	14,277
Inter-Segment
Segment information
Sales									(855)	(880)	(867)
Inter-Segment | Other
Segment information
Sales									855	880	867
Contract Drilling:
Segment information
Sales									1,610,957	3,147,515	3,702,558
Segment Operating Income (Loss)									75,691	759,284	1,130,859
Depreciation									577,834	588,943	508,601
Total assets	5,597,632				6,113,743				5,597,632	6,113,743	5,991,936
Additions to Long-Lived Assets									221,214	1,005,723	1,018,703
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									75,691	759,284	1,130,859
Contract Drilling: | U.S. Land
Segment information
Sales									1,242,462	2,523,518	3,099,954
Segment Operating Income (Loss)									74,118	698,375	1,025,745
Depreciation									508,237	519,950	455,934
Total assets	5,005,299				5,429,179				5,005,299	5,429,179	5,261,361
Additions to Long-Lived Assets									209,156	949,978	930,263
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									74,118	698,375	1,025,745
Contract Drilling: | Offshore
Segment information
Sales									138,601	241,666	251,341
Segment Operating Income (Loss)									15,659	68,002	69,969
Depreciation									12,495	11,659	12,300
Total assets	105,152				118,852				105,152	118,852	137,104
Additions to Long-Lived Assets									9,694	16,100	4,372
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									15,659	68,002	69,969
Contract Drilling: | International Land
Segment information
Sales									229,894	382,331	351,263
Segment Operating Income (Loss)									(14,086)	(7,093)	35,145
Depreciation									57,102	57,334	40,367
Total assets	$ 487,181				$ 565,712				487,181	565,712	593,471
Additions to Long-Lived Assets									2,364	39,645	84,068
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income									(14,086)	(7,093)	35,145
Contract Drilling: | Operating segment
Segment information
Sales									1,610,957	3,147,515	3,702,558
Contract Drilling: | Operating segment | U.S. Land
Segment information
Sales									1,242,462	2,523,518	3,099,954
Contract Drilling: | Operating segment | Offshore
Segment information
Sales									138,601	241,666	251,341
Contract Drilling: | Operating segment | International Land
Segment information
Sales									$ 229,894	$ 382,331	$ 351,263