Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment information
External Sales	$ 840,197	$ 819,785	$ 2,523,078	$ 2,322,355
Total operating revenues	840,197	819,785	2,523,078	2,322,355
Segment Operating Income (Loss)	256,504	247,518	763,652	707,549
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	256,504	247,518	763,652	707,549
Income from asset sales	4,006	1,862	14,538	14,365
Corporate general and administrative costs and corporate depreciation	(20,550)	(16,725)	(64,763)	(51,695)
Operating income from continuing operations	239,960	232,655	713,427	670,219
Other income (expense):
Interest and dividend income	341	329	1,082	1,021
Interest expense	(2,091)	(2,411)	(4,585)	(7,293)
Gain on sale of investment securities	153,369		162,121
Other	(1,214)	309	(3,195)	288
Total other income (expense)	150,405	(1,773)	155,423	(5,984)
Income from continuing operations before income taxes	390,365	230,882	868,850	664,235
Contract Drilling
Segment information
External Sales	836,653	815,885	2,513,075	2,311,504
Total operating revenues	836,653	815,885	2,513,075	2,311,504
Segment Operating Income (Loss)	258,968	249,679	770,290	713,331
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	258,968	249,679	770,290	713,331
U.S. Land
Segment information
External Sales	695,816	706,786	2,077,556	1,983,369
Total operating revenues	695,816	706,786	2,077,556	1,983,369
Segment Operating Income (Loss)	236,388	235,684	696,774	670,349
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	236,388	235,684	696,774	670,349
Offshore
Segment information
External Sales	53,859	41,617	167,182	135,830
Total operating revenues	53,859	41,617	167,182	135,830
Segment Operating Income (Loss)	14,122	7,720	42,778	29,742
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	14,122	7,720	42,778	29,742
International Land
Segment information
External Sales	86,978	67,482	268,337	192,305
Total operating revenues	86,978	67,482	268,337	192,305
Segment Operating Income (Loss)	8,458	6,275	30,738	13,240
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	8,458	6,275	30,738	13,240
Other
Segment information
External Sales	3,544	3,900	10,003	10,851
Inter-Segment	214	209	643	629
Total operating revenues	3,758	4,109	10,646	11,480
Segment Operating Income (Loss)	(2,464)	(2,161)	(6,638)	(5,782)
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	(2,464)	(2,161)	(6,638)	(5,782)
Reportable and other
Segment information
External Sales	840,197	819,785	2,523,078	2,322,355
Inter-Segment	214	209	643	629
Total operating revenues	840,411	819,994	2,523,721	2,322,984
Segment Operating Income (Loss)	256,504	247,518	763,652	707,549
Reconciliation of segment operating income to income from continuing operations before income taxes
Segment operating income	256,504	247,518	763,652	707,549
Eliminations
Segment information
Inter-Segment	(214)	(209)	(643)	(629)
Total operating revenues	$ (214)	$ (209)	$ (643)	$ (629)