CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 86,492	$ 54,921
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,026	7,856
Share-based compensation	25,132	23,145
Deferred income taxes	(298)	(1,016)
Net gain on marketable securities	(1,768)	(944)
Non-cash operating lease costs	4,000	4,493
Provision for doubtful accounts, net	219	281
Net loss on sales and abandonment of property and equipment	62	48
Gain on sale of product line assets	(7,334)	0
Changes in operating assets and liabilities:
Accounts receivable	33,130	22,391
Prepaid expenses and other assets	(7,310)	(21,711)
Accounts payable	(1,479)	10,349
Accrued compensation and employee benefits	(46,704)	(35,566)
Other liabilities	(12,241)	(4,379)
Deferred revenue	(980)	497
Net cash provided by operating activities	77,947	60,365
Cash flows from investing activities:
Purchases of property and equipment	(3,045)	(6,500)
Proceeds from sales of marketable securities	567	167
Purchases of marketable securities	(1,741)	(2,733)
Proceeds from sale of product line assets	8,291	0
(Purchase of) distribution from equity investment	(210)	55
Net cash provided by (used in) investing activities	3,862	(9,011)
Cash flows from financing activities:
Proceeds from revolving line of credit	116,000	117,000
Payments on revolving line of credit	(80,000)	(367,000)
Proceeds from issuance of senior notes	0	350,000
Payments on debt issuance costs	0	(6,805)
Payments on finance leases	(176)	(425)
Proceeds from issuance of treasury stock under employee stock plans	57	5,091
Taxes paid related to net share settlement of equity awards	(85,678)	(86,047)
Repurchases of common stock	(50,011)	(60,009)
Net cash used in financing activities	(99,808)	(48,195)
Effect of exchange rate changes on cash	5,267	1,631
Increase (decrease) in cash and cash equivalents	(12,732)	4,790
Cash and cash equivalents, beginning of period	157,394	106,426
Cash and cash equivalents, end of period	144,662	111,216
Supplemental disclosures of cash flow information:
Cash paid for income taxes, net of refunds of $221 and $154 during the quarters ended December 31, 2020, and 2019, respectively	3,186	2,391
Interest Paid, Excluding Capitalized Interest, Operating Activities	17,858	12,856
Supplemental disclosures of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable	13	93
Finance lease obligations incurred	$ 0	$ 3,045