CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 27,299	$ 37,901
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,731	9,058
Share-based compensation	16,510	14,519
Deferred income taxes	6,717	0
Net gain on marketable securities	(90)	0
Provision for doubtful accounts, net	0	463
Net loss on sales of property and equipment	9	0
Changes in operating assets and liabilities:
Accounts receivable	4,656	8,253
Prepaid expenses and other assets	(6,527)	(16,876)
Accounts payable	(119)	(725)
Accrued compensation and employee benefits	(28,672)	(29,030)
Other liabilities	(1,174)	(2,091)
Deferred revenue	2,437	11,506
Net cash provided by operating activities	28,777	32,978
Cash flows from investing activities:
Purchases of property and equipment	(4,044)	(4,319)
Proceeds from sales of marketable securities	8	0
Purchases of marketable securities	(1,943)	0
Net cash used in investing activities	(5,979)	(4,319)
Cash flows from financing activities:
Proceeds from revolving line of credit	79,000	60,000
Payments on revolving line of credit	(20,000)	(10,000)
Payments on debt issuance costs	(240)	0
Proceeds from issuance of treasury stock under employee stock plans	693	3,663
Taxes paid related to net share settlement of equity awards	(38,867)	(35,598)
Dividends paid	0	(618)
Repurchases of common stock	(55,263)	(30,442)
Net cash used in financing activities	(34,677)	(12,995)
Effect of exchange rate changes on cash	474	(3,489)
Increase (decrease) in cash and cash equivalents	(11,405)	12,175
Cash and cash equivalents, beginning of period	105,618	75,926
Cash and cash equivalents, end of period	94,213	88,101
Supplemental disclosures of cash flow information:
Cash paid for income taxes, net of refunds	2,221	7,463
Cash paid for interest	7,087	5,851
Supplemental disclosures of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable	$ 1,482	$ 3,816