CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 59,574	$ 62,985
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,095	18,236
Share-based compensation	35,749	29,231
Deferred income taxes	6,041	0
Net gain on marketable securities	(198)	0
Provision for doubtful accounts, net	482	925
Net loss on sales of property and equipment	27	10
Changes in operating assets and liabilities:
Accounts receivable	(17,582)	23,710
Prepaid expenses and other assets	(6,225)	(27,415)
Accounts payable	(515)	(3,534)
Accrued compensation and employee benefits	(20,650)	(22,671)
Other liabilities	(252)	(3,487)
Deferred revenue	6,464	21,407
Net cash provided by operating activities	78,010	99,397
Cash flows from investing activities:
Purchases of property and equipment	(11,111)	(9,604)
Proceeds from sales of marketable securities	2,383	0
Purchases of marketable securities	(4,528)	0
Net cash used in investing activities	(13,256)	(9,604)
Cash flows from financing activities:
Proceeds from revolving line of credit	147,000	79,000
Payments on revolving line of credit	(48,000)	(24,000)
Payments on debt issuance costs	(240)	0
Proceeds from issuance of treasury stock under employee stock plans	1,706	9,114
Taxes paid related to net share settlement of equity awards	(40,448)	(36,914)
Dividends paid	0	(1,238)
Repurchases of common stock	(124,715)	(74,647)
Net cash used in financing activities	(64,697)	(48,685)
Effect of exchange rate changes on cash	2,193	(1,186)
Increase in cash and cash equivalents	2,250	39,922
Cash and cash equivalents, beginning of period	105,618	75,926
Cash and cash equivalents, end of period	107,868	115,848
Supplemental disclosures of cash flow information:
Cash paid for income taxes, net of refunds	6,669	21,557
Cash paid for interest	13,324	12,377
Supplemental disclosures of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable	6,006	2,757
Repurchases of Common Stock Incurred Not Yet Paid	$ 5,557	$ 0