CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Adoption of ASC	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Adoption of ASC	Accumulated Other Comprehensive Loss	Treasury Stock	Noncontrolling Interest	Noncontrolling Interest Adoption of ASC
Beginning balance at Sep. 30, 2018	$ 3,049,961	$ (2,584)	$ 2,836	$ 4,715,473	$ 3,720,582	$ (1,482)	$ (79,253)	$ (5,426,814)	$ 117,137	$ (1,102)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	721,828				722,746				(918)
Other comprehensive (loss) income	(4,972)						(7,630)		2,658
Cash dividends	(255,064)				(255,064)
Exercises of stock options	54,860		11	54,849
Share-based compensation expense	48,431			48,431
Purchases of common stock	(498,886)							(498,886)
Employee tax withholdings related to restricted share vesting	(5,959)							(5,959)
Other	(418)		2	(420)
Ending balance at Jun. 30, 2019	$ 3,107,197		2,849	4,818,333	4,186,782		(86,883)	(5,931,659)	117,775
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member
Cash dividends (in dollars per share)	$ 1.20
Beginning balance at Mar. 31, 2019	$ 3,038,331		2,846	4,790,507	3,969,459		(85,142)	(5,756,455)	117,116
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	302,002				301,959				43
Other comprehensive (loss) income	(1,125)						(1,741)		616
Cash dividends	(84,636)				(84,636)
Exercises of stock options	17,270		3	17,267
Share-based compensation expense	10,562			10,562
Purchases of common stock	(174,912)							(174,912)
Employee tax withholdings related to restricted share vesting	(292)							(292)
Other	(3)			(3)
Ending balance at Jun. 30, 2019	$ 3,107,197		2,849	4,818,333	4,186,782		(86,883)	(5,931,659)	117,775
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends (in dollars per share)	$ 0.40
Beginning balance at Sep. 30, 2019	$ 2,993,206	$ 35,138	2,853	4,850,142	4,235,491	$ 35,138	(111,965)	(6,097,604)	114,289	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,444,947				1,437,356				7,591
Other comprehensive (loss) income	(27,880)						(16,699)		(11,181)
Cash dividends	(256,764)				(256,764)
Exercises of stock options	137,748		18	137,730
Share-based compensation expense	57,579			57,579
Purchases of common stock	(405,692)							(405,692)
Employee tax withholdings related to restricted share vesting	(9,660)							(9,660)
Other	(671)		4	(675)
Ending balance at Jun. 30, 2020	$ 3,967,951		2,875	5,044,776	5,451,221		(128,664)	(6,512,956)	110,699
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Cash dividends (in dollars per share)	$ 1.24
Beginning balance at Mar. 31, 2020	$ 3,705,113		2,868	4,972,109	5,248,005		(132,808)	(6,499,584)	114,523
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	287,268				289,439				(2,171)
Other comprehensive (loss) income	2,491						4,144		(1,653)
Cash dividends	(86,223)				(86,223)
Exercises of stock options	60,991		7	60,984
Share-based compensation expense	11,816			11,816
Purchases of common stock	(13,297)							(13,297)
Employee tax withholdings related to restricted share vesting	(75)							(75)
Other	(133)			(133)
Ending balance at Jun. 30, 2020	$ 3,967,951		$ 2,875	$ 5,044,776	$ 5,451,221		$ (128,664)	$ (6,512,956)	$ 110,699
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends (in dollars per share)	$ 0.42