CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Noncontrolling Interest
Beginning balance at Sep. 30, 2017	$ 2,064,461	$ 2,806	$ 4,517,635	$ 2,395,218	$ (95,850)	$ (4,755,348)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	861,853			861,853
Other comprehensive income (loss)	(488)				(488)
Cash dividends	(83,555)			(83,555)
Exercises of stock options	29,574	6	29,568
Share-based compensation expense	32,608		32,608
Purchases of common stock	(22,496)					(22,496)
Employee tax withholdings related to restricted share vesting	(7,375)					(7,375)
Other	0	2	(2)
Ending balance at Dec. 31, 2017	2,874,582	2,814	4,579,809	3,173,516	(96,338)	(4,785,219)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASC 606 | ASC 606	(2,584)	0	0	(1,482)	0	0	(1,102)
Beginning balance at Sep. 30, 2018	3,049,961	2,836	4,715,473	3,720,582	(79,253)	(5,426,814)	117,137
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	391,753			393,652			(1,899)
Other comprehensive income (loss)	(11,486)				(13,630)		2,144
Cash dividends	(85,535)			(85,535)
Exercises of stock options	22,400	4	22,396
Share-based compensation expense	31,768		31,768
Purchases of common stock	(225,850)					(225,850)
Employee tax withholdings related to restricted share vesting	(5,654)					(5,654)
Other	(40)	2	(42)
Ending balance at Dec. 31, 2018	$ 3,164,733	$ 2,842	$ 4,769,595	$ 4,027,217	$ (92,883)	$ (5,658,318)	$ 116,280