CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 236,411	$ 192,124	$ 126,482
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	30,367	31,612	30,182
Share-based compensation	93,681	82,973	74,814
Deferred income taxes	(8,639)	7,701	10,584
Non-cash operating lease costs	20,011
Impairment loss on operating lease assets	28,016
Provision of doubtful accounts	3,199	518	623
Net gain (loss) on marketable securities	(2,071)	761	(1,449)
Gain on sale of equity investments	0	0	(10,000)
Net loss on sales and abandonment of property and equipment	5,249	127	231
Changes in operating assets and liabilities:
Accounts receivable	(59,889)	(36,176)	(8,266)
Prepaid expenses and other assets	(960)	(55,507)	(9,790)
Accounts payable	1,059	1,885	843
Accrued compensation and employee benefits	12,065	22,380	7,352
Other liabilities	693	1,463	6,246
Deferred revenue	5,724	10,489	(4,800)
Net cash provided by operating activities	364,916	260,350	223,052
Cash flows from investing activities:
Purchases of property and equipment	(21,989)	(23,981)	(31,299)
Proceeds from sales of marketable securities	3,470	3,480	3,230
Purchases of marketable securities	(6,119)	(6,404)	(6,050)
Distribution from equity investments	0	0	20,000
Distribution from equity investments	55	0	0
Cash paid for acquisitions, net of cash acquired	0	(15,855)	0
Net cash used in investing activities	(24,583)	(42,760)	(14,119)
Cash flows from financing activities:
Proceeds from revolving line of credit	263,000	229,000	427,000
Payments on revolving line of credit	(513,000)	(141,000)	(531,000)
Proceeds from issuance of senior notes	350,000	0	400,000
Payments on senior notes	(85,000)	(28,000)	(131,000)
Payments on debt issuance costs	(6,840)	0	(7,849)
Payments on finance leases	(1,716)	(945)	0
Proceeds from issuance of treasury stock under employee stock plans	42,258	22,788	11,023
Taxes paid related to net share settlement of equity awards	(102,903)	(52,996)	(44,205)
Repurchases of common stock	(235,223)	(228,894)	(342,596)
Net cash used in financing activities	(289,424)	(200,047)	(218,627)
Effect of exchange rate changes on cash	59	(1,140)	(5,901)
Increase (decrease) in cash and cash equivalents	50,968	16,403	(15,595)
Cash and cash equivalents, beginning of year	106,426	90,023	105,618
Cash and cash equivalents, end of year	157,394	106,426	90,023
Supplemental disclosures of cash flow information:
Cash paid for income taxes, net of refunds of $1,931, $1,372 and $3,079 during the years ended September 30, 2020, 2019 and 2018, respectively	10,152	18,779	13,398
Cash paid for interest	37,735	39,924	26,106
Supplemental disclosures of non-cash investing and financing activities:
Finance lease obligation incurred	1,387	5,803	0
Purchase of property and equipment included in accounts payable	$ 166	$ 1,448	$ 1,913