Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Segment information
External Sales	$ 844,572	$ 732,588
Total operating revenues	844,572	732,588
Segment Operating Income (Loss)	256,870	243,061
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	256,870	243,061
Income from asset sales	5,219	4,683
Corporate general and administrative costs and corporate depreciation	(21,542)	(17,205)
Operating income from continuing operations	240,547	230,539
Other income (expense):
Interest and dividend income	426	336
Interest expense	(1,308)	(2,461)
Gain on sale of investment securities	8,752
Other	(2,084)	21
Total other income (expense)	5,786	(2,104)
Income from continuing operations before income taxes	246,333	228,435
Contract Drilling
Segment information
External Sales	841,015	729,306
Total operating revenues	841,015	729,306
Segment Operating Income (Loss)	258,505	244,849
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	258,505	244,849
U.S. Land
Segment information
External Sales	696,030	617,779
Total operating revenues	696,030	617,779
Segment Operating Income (Loss)	234,388	224,706
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	234,388	224,706
Offshore
Segment information
External Sales	57,718	50,792
Total operating revenues	57,718	50,792
Segment Operating Income (Loss)	15,006	12,204
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	15,006	12,204
International Land
Segment information
External Sales	87,267	60,735
Total operating revenues	87,267	60,735
Segment Operating Income (Loss)	9,111	7,939
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	9,111	7,939
Other.
Segment information
External Sales	3,557	3,282
Intersegment sales	215	210
Total operating revenues	3,772	3,492
Segment Operating Income (Loss)	(1,635)	(1,788)
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	(1,635)	(1,788)
Reportable and other
Segment information
External Sales	844,572	732,588
Intersegment sales	215	210
Total operating revenues	844,787	732,798
Segment Operating Income (Loss)	256,870	243,061
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	256,870	243,061
Eliminations
Segment information
Intersegment sales	(215)	(210)
Total operating revenues	$ (215)	$ (210)