Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income (loss)	$ 51,987	$ 6,239	$ (54,465)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Stock-based compensation	82,939	76,708	65,996
Depreciation and amortization	87,408	86,742	86,554
Benefit from deferred income taxes	(56,556)	(28,289)	(44,182)
Other non-cash costs, net	534	2,272	966
Changes in operating assets and liabilities, excluding the effects of acquisitions:
Accounts receivable	20,396	12,832	52,617
Accounts payable and accrued expenses	5,251	20,315	(14,185)
Accrued compensation and benefits	(6,988)	(34,846)	60,944
Deferred revenue	56,141	5,808	16,232
Accrued income taxes, net of income tax receivable	10,323	(798)	6,749
Other current assets and prepaid expenses	(10,583)	721	4,591
Other noncurrent assets and liabilities	6,959	(12,470)	1,444
Net cash provided by operating activities	247,811	135,234	183,261
Cash flows from investing activities:
Additions to property and equipment	(36,041)	(25,444)	(26,189)
Purchases of short- and long-term marketable securities	(24,311)	(19,726)	(44,605)
Proceeds from maturities of short- and long-term marketable securities	18,140	18,785	0
Acquisitions of businesses, net of cash acquired	(3,000)	(4,960)	(165,802)
Purchases of investments	(1,000)	0	(560)
Proceeds from sales of investments	0	15,218	0
Purchase of intangible asset	(3,000)	0	0
Net cash used by investing activities	(49,212)	(16,127)	(237,156)
Cash flows from financing activities:
Borrowings under credit facility and senior notes	250,000	150,000	670,000
Repayments of borrowings under credit facility	(320,000)	(190,000)	(580,000)
Repurchases of common stock	(1,100,000)	(50,991)	0
Proceeds from issuance of common stock	1,015,654	10,778	21
Payments of withholding taxes in connection with vesting of stock-based awards	(45,374)	(26,654)	(20,939)
Credit facility origination costs	(2,851)	(184)	(6,855)
Contingent consideration	(8,275)	(11,054)	(10,621)
Net cash provided (used) by financing activities	(210,846)	(118,105)	51,606
Effect of exchange rate changes on cash and cash equivalents	(7,810)	1,066	6,807
Net increase (decrease) in cash and cash equivalents	(20,057)	2,068	4,518
Cash and cash equivalents, beginning of year	280,003	277,935	273,417
Cash and cash equivalents, end of year	259,946	280,003	277,935
Supplemental disclosure of non-cash financing activities:
Fair value of contingent consideration recorded for acquisitions	$ 2,100	$ 0	$ 16,900