Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net income	$ 307,441	$ 427,734	$ 453,689
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	201,948	162,914	157,855
Depreciation and amortization	95,857	68,507	59,491
Non-cash operating lease costs	39,139	0	0
Deferred income taxes	7,293	7,440	20,810
Impairment of assets	9,673	6,273	0
Non-cash provisions for exit costs	0	8,211	0
Other	2,122	1,662	1,194
Changes in operating assets and liabilities (excluding effects of the acquisition of businesses):
Accounts receivable	46,502	(18,305)	(4,889)
Inventories	6,503	(3,832)	(734)
Other current assets	(49,895)	(75,449)	15,607
Other assets	(25,690)	(22,742)	446
Accounts payable and accrued liabilities	34,742	74,710	6,583
Deferred revenue	35,514	110,718	51,016
Lease liabilities	(50,251)	0	0
Net cash provided by operating activities	660,898	747,841	761,068
Investing activities
Purchases of investments	(584,240)	(602,987)	(855,424)
Maturities of investments	543,065	625,201	439,130
Sales of investments	309,687	278,244	12,736
Acquisition of businesses, net of cash acquired	(955,574)	(611,550)	0
Cash provided by sale of fixed assets	0	0	1,000
Purchases of property and equipment	(59,940)	(103,542)	(53,465)
Net cash used in investing activities	(747,002)	(414,634)	(456,023)
Financing activities
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan	52,835	45,598	48,818
Repurchase of common stock	(100,016)	(201,045)	(600,081)
Proceeds from term debt agreement	400,000	0	0
Payments on term debt agreement	(10,000)	0	0
Payments for debt issuance costs	(3,040)	0	0
Taxes paid related to net share settlement of equity awards	(2,536)	0	0
Net cash provided by (used in) financing activities	337,243	(155,447)	(551,263)
Net increase (decrease) in cash, cash equivalents and restricted cash	251,139	177,760	(246,218)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(567)	(1,400)	(2,340)
Cash, cash equivalents and restricted cash, beginning of year	602,254	425,894	674,452
Cash, cash equivalents and restricted cash, end of year	852,826	602,254	425,894
Supplemental disclosures of cash flow information
Cash paid for taxes, net of refunds	80,236	100,569	104,878
Cash paid for amounts included in the measurement of operating lease liabilities	60,564	0	0
Cash paid for interest on long-term debt	6,568	0	0
Supplemental disclosures of non-cash activities
Right-of-use assets obtained in exchange for lease obligations	402,007	0	0
Capitalized leasehold improvements paid directly by landlord	$ 0	$ 34,948	$ 9,958