CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Noncontrolling Interest [Member]	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Sep. 30, 2016		291,384			3,751
Beginning balance at Sep. 30, 2016	$ 1,931,330	$ 291	$ 2,492,992		$ (16,788)	$ (116,134)	$ (429,031)
Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans (in shares)		10,709
Issuance of common stock under employee stock plans	17,383	$ 11	17,372
Cancellation of restricted stock, and repurchase of common stock at cost for employee tax withholding (in shares)		3,377
Cancellation of restricted stock, and repurchase of common stock at cost for employee tax withholding	(55,132)	$ (3)	(55,129)
Stock-based compensation	$ 160,575		160,575
Repurchase of common stock (in shares)	(5,800)	(5,797)
Repurchase of common stock	$ (99,077)	$ (6)	(99,071)				0
Issuance of common stock in connection with business and asset acquisitions (in shares)		1,019
Issuance of common stock in connection with business and asset acquisitions	16,347	$ 1	16,346
Equity portion of convertible debt issuance, net of tax effect	96,160		96,160
Net income (loss)	(150,996)						(150,996)
Other comprehensive income (loss)	14,792					14,792
Ending balance (in shares) at Sep. 30, 2017		293,938			3,751
Ending balance at Sep. 30, 2017	1,931,382	$ 294	2,629,245		$ (16,788)	(101,342)	(580,027)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	(882)						(882)
Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans (in shares)		10,568
Issuance of common stock under employee stock plans	18,384	$ 10	18,374
Cancellation of restricted stock, and repurchase of common stock at cost for employee tax withholding (in shares)		3,304
Cancellation of restricted stock, and repurchase of common stock at cost for employee tax withholding	(52,336)	$ (3)	(52,333)
Stock-based compensation	$ 138,487		138,487
Repurchase of common stock (in shares)	(9,700)	(9,698)
Repurchase of common stock	$ (136,090)	$ (10)	(136,080)
Stock Issued During Period, Value, Other	2,900
Net income (loss)	(159,928)						(159,928)
Other comprehensive income (loss)	(21,521)					(21,521)
Ending balance (in shares) at Sep. 30, 2018		291,504			3,751
Ending balance at Sep. 30, 2018	1,717,496	$ 291	2,597,693		$ (16,788)	(122,863)	(740,837)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,717,496
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	233,415						233,415
Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans (in shares)		8,981
Issuance of common stock under employee stock plans	16,597	$ 9	16,588
Cancellation of restricted stock, and repurchase of common stock at cost for employee tax withholding (in shares)		(2,645)
Cancellation of restricted stock, and repurchase of common stock at cost for employee tax withholding	(42,554)	$ (2)	(42,552)
Stock-based compensation	$ 161,371		161,371
Repurchase of common stock (in shares)	(8,200)	(8,160)
Repurchase of common stock	$ (126,938)	$ (8)	(126,930)				0
Noncontrolling Interest, Decrease from Deconsolidation			(8,281)	$ 18,144
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	9,863
Net income (loss)	213,810
Other comprehensive income (loss)	(9,910)					(9,910)
Ending balance (in shares) at Sep. 30, 2019		289,680			3,751
Ending balance at Sep. 30, 2019	2,155,006	$ 290	$ 2,597,889	$ 18,144	$ (16,788)	$ (132,773)	$ (293,612)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,173,150