CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 40,007	$ 32,879
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,967	7,731
Share-based compensation	21,854	16,510
Deferred income taxes	(50)	(1,942)
Net (gain) loss on marketable securities	3,050	(90)
Provision for doubtful accounts, net	180	0
Net (gain) loss on sales of property and equipment	(22)	9
Changes in operating assets and liabilities:
Accounts receivable	18,191	4,516
Prepaid expenses and other assets	(10,787)	(6,315)
Accounts payable	1,671	(119)
Accrued compensation and employee benefits	(28,918)	(28,672)
Other liabilities	(4,848)	(1,267)
Deferred revenue	562	5,537
Net cash provided by operating activities	48,857	28,777
Cash flows from investing activities:
Purchases of property and equipment	(6,474)	(4,044)
Proceeds from sales of marketable securities	102	8
Purchases of marketable securities	(2,303)	(1,943)
Net cash used in investing activities	(8,675)	(5,979)
Cash flows from financing activities:
Proceeds from revolving line of credit	103,000	79,000
Payments on revolving line of credit	(35,000)	(20,000)
Payments on debt issuance costs	0	(240)
Proceeds from issuance of treasury stock under employee stock plans	7,550	693
Taxes paid related to net share settlement of equity awards	(42,987)	(38,867)
Repurchases of common stock	(82,700)	(55,263)
Net cash used in financing activities	(50,137)	(34,677)
Effect of exchange rate changes on cash	(172)	474
Decrease in cash and cash equivalents	(10,127)	(11,405)
Cash and cash equivalents, beginning of period	90,023	105,618
Cash and cash equivalents, end of period	79,896
Supplemental disclosures of cash flow information:
Cash paid for income taxes, net of refunds	1,394	2,221
Cash paid for interest	13,439	7,087
Supplemental disclosures of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable	$ 433	$ 1,482