Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net income	$ 88,429	$ 94,218
Adjustments to reconcile net income to net cash provided by operating activities:
Realized loss on disposition of assets and investments	49	30
Stock-based compensation	40,948	46,611
Provisions for doubtful accounts and sales returns	593	291
Depreciation and amortization	15,180	14,887
Deferred income taxes	14,226	(2,945)
Changes in operating assets and liabilities:
Accounts receivable	238	(45,327)
Inventories	722	374
Other current assets	11,517	(306)
Other assets	(696)	391
Accounts payable and accrued liabilities	(8,216)	37,082
Deferred revenue	26,967	44,006
Net cash provided by operating activities	189,957	189,312
Investing activities
Purchases of investments	(238,632)	(98,983)
Maturities of investments	113,771	105,744
Sales of investments	9,248	11,211
(Increase) decrease in restricted cash	(21)	32
Cash provided by sale of fixed asset	1,000	0
Acquisition of intangible assets	0	(4,000)
Purchases of property and equipment	(6,491)	(14,133)
Net cash used in investing activities	(121,125)	(129)
Financing activities
Excess tax benefit from stock-based compensation	0	2,940
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan	19,915	18,836
Repurchase of common stock	(150,025)	(150,021)
Net cash used in financing activities	(130,110)	(128,245)
Net increase in cash and cash equivalents	(61,278)	60,938
Effect of exchange rate changes on cash and cash equivalents	46	(2,575)
Cash and cash equivalents, beginning of period	673,228	514,571
Cash and cash equivalents, end of period	$ 611,996	$ 572,934