Consolidated Statement Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Accumulated Other Comprehensive Loss	Retained Earnings
Balance, shares at Sep. 30, 2017		62,594,000
Balance at Sep. 30, 2017	$ 1,229,392	$ 17,627	$ (17,997)	$ 1,229,762
Exercise of employee stock options	3	$ 3
Exercise of employee stock options, shares		1,000
Issuance of stock under employee stock purchase plan	48,815	$ 48,815
Issuance of stock under employee stock purchase plan, shares		475,000
Issuance of restricted stock, shares		1,219,000
Repurchase of common stock	(600,081)	$ (203,873)		(396,208)
Repurchase of common stock, shares		(4,074,000)
Taxes paid related to net share settlement of equity awards	0
Stock-based compensation	157,855	$ 157,855
Net income	453,689			453,689
Other comprehensive income (loss)	(4,181)		(4,181)
Balance, shares at Sep. 30, 2018		60,215,000
Balance at Sep. 30, 2018	1,285,492	$ 20,427	(22,178)	1,287,243
Exercise of employee stock options	159	$ 159
Exercise of employee stock options, shares		6,000
Issuance of stock under employee stock purchase plan	45,439	$ 45,439
Issuance of stock under employee stock purchase plan, shares		334,000
Issuance of restricted stock, shares		998,000
Repurchase of common stock	(201,045)	$ (88,110)		(112,935)
Repurchase of common stock, shares		(1,186,000)
Taxes paid related to net share settlement of equity awards	0
Stock-based compensation	164,682	$ 164,682
Net income	427,734			427,734
Other comprehensive income (loss)	$ 2,988		2,988
Balance, shares at Sep. 30, 2019	60,367,000	60,367,000
Balance at Sep. 30, 2019	$ 1,761,497	$ 142,597	(19,190)	1,638,090
Exercise of employee stock options	$ 2,596	$ 2,596
Exercise of employee stock options, shares	104,487	104,000
Issuance of stock under employee stock purchase plan	$ 50,239	$ 50,239
Issuance of stock under employee stock purchase plan, shares		419,000
Issuance of restricted stock, shares		1,027,000
Repurchase of common stock	$ (100,016)	$ (100,016)
Repurchase of common stock, shares	(799,495)	(799,000)
Taxes paid related to net share settlement of equity awards	$ (2,536)	$ (2,536)
Taxes paid related to net share settlement of equity awards, shares		(19,000)
Stock-based compensation	212,573	$ 212,573
Net income	307,441			307,441
Other comprehensive income (loss)	$ 474		474
Balance, shares at Sep. 30, 2020	61,099,000	61,099,000
Balance at Sep. 30, 2020	$ 2,232,268	$ 305,453	$ (18,716)	$ 1,945,531