Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income (loss)	$ 6,239	$ (54,465)	$ 47,557
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Stock-based compensation	76,708	65,996	50,182
Depreciation and amortization	86,742	86,554	84,433
Benefit from deferred income taxes	(28,289)	(44,182)	(49,361)
Excess tax benefits realized from stock-based awards	(644)	(93)	(24)
Pension settlement loss	0	0	66,332
Other non-cash costs, net	2,272	966	157
Changes in operating assets and liabilities, excluding the effects of acquisitions:
Accounts receivable	12,832	52,617	29,723
Accounts payable and accrued expenses	20,315	(14,185)	31,134
Accrued compensation and benefits	(34,846)	60,944	(56,950)
Deferred revenue	5,808	16,232	8,852
Accrued income taxes, net of income tax receivable	(798)	6,749	(3,536)
Other current assets and prepaid expenses	721	4,591	(10,716)
Other noncurrent assets and liabilities	(12,470)	1,444	(17,880)
Net cash provided by operating activities	134,590	183,168	179,903
Cash flows from investing activities:
Additions to property and equipment	(25,444)	(26,189)	(30,628)
Purchases of short- and long-term marketable securities	(19,726)	(44,605)	0
Proceeds from maturities of short- and long-term marketable securities	18,785	0	0
Acquisitions of businesses, net of cash acquired	(4,960)	(165,802)	(98,411)
Purchases of investments	0	(560)	(11,000)
Proceeds from sales of investments	15,218	0	0
Net cash used by investing activities	(16,127)	(237,156)	(140,039)
Cash flows from financing activities:
Borrowings under credit facility and senior notes	150,000	670,000	185,000
Repayments of borrowings under credit facility	(190,000)	(580,000)	(128,750)
Repurchases of common stock	(50,991)	0	(64,940)
Proceeds from issuance of common stock	10,778	21	41
Excess tax benefits realized from stock-based awards	644	93	24
Payments of withholding taxes in connection with vesting of stock-based awards	(26,654)	(20,939)	(29,207)
Credit facility origination costs	(184)	(6,855)	0
Contingent consideration	(11,054)	(10,621)	(4,323)
Net cash provided (used) by financing activities	(117,461)	51,699	(42,155)
Effect of exchange rate changes on cash and cash equivalents	1,066	6,807	(17,946)
Net increase (decrease) in cash and cash equivalents	2,068	4,518	(20,237)
Cash and cash equivalents, beginning of year	277,935	273,417	293,654
Cash and cash equivalents, end of year	280,003	277,935	273,417
Supplemental disclosure of non-cash financing activities:
Fair value of contingent consideration recorded for acquisitions	$ 0	$ 16,900	$ 3,800