CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 73,388	$ 64,048
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,786	15,095
Share-based compensation	42,336	35,749
Deferred income taxes	74	(3,152)
Net (gain) loss on marketable securities	1,300	(198)
Provision for doubtful accounts, net	391	482
Net (gain) loss on sales of property and equipment	(5)	27
Changes in operating assets and liabilities:
Accounts receivable	(5,015)	(9,019)
Prepaid expenses and other assets	(12,219)	(5,904)
Accounts payable	(2,210)	(515)
Accrued compensation and employee benefits	(16,970)	(20,650)
Other liabilities	(2,672)	(418)
Deferred revenue	2,462	2,465
Net cash provided by operating activities	96,646	78,010
Cash flows from investing activities:
Purchases of property and equipment	(10,644)	(11,111)
Proceeds from sales of marketable securities	2,267	2,383
Purchases of marketable securities	(4,396)	(4,528)
Net cash used in investing activities	(12,773)	(13,256)
Cash flows from financing activities:
Proceeds from revolving line of credit	138,000	147,000
Payments on revolving line of credit	(80,000)	(48,000)
Payments on debt issuance costs	0	(240)
Proceeds from issuance of treasury stock under employee stock plans	12,850	1,706
Taxes paid related to net share settlement of equity awards	(48,470)	(40,448)
Repurchases of common stock	(119,723)	(124,715)
Net cash used in financing activities	(97,343)	(64,697)
Effect of exchange rate changes on cash	332	2,193
Increase (decrease) in cash and cash equivalents	(13,138)	2,250
Cash and cash equivalents, beginning of period	90,023	105,618
Cash and cash equivalents, end of period	76,885	107,868
Supplemental disclosures of cash flow information:
Cash paid for income taxes, net of refunds	7,962	6,669
Cash paid for interest	19,686	13,324
Supplemental disclosures of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable	77	6,006
Unsettled repurchases of common stock	$ 0	$ 5,557