Fair Value Measurements (Schedule of Financial Assets and Liabilities Measured at Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017	Jul. 01, 2017	Sep. 30, 2016
Financial assets:
Cash equivalents	$ 85,382	$ 49,845
Marketable securities	54,172	50,315
Forward contracts	4,956	1,163
Financial assets, fair value	144,510	101,323
Financial liabilities:
Contingent consideration related to acquisitions	2,100	8,400
Forward contracts	1,190	4,347
Liabilities, Fair Value Disclosure, Recurring	3,290	12,747
Level 1
Financial assets:
Cash equivalents	85,382	49,845
Financial assets, fair value	138,344	97,518
Level 2
Financial assets:
Forward contracts	4,956	1,163
Financial assets, fair value	6,166	3,805
Financial liabilities:
Forward contracts	1,190	4,347
Liabilities, Fair Value Disclosure, Recurring	1,190	4,347
Level 3
Financial liabilities:
Contingent consideration related to acquisitions	2,100	8,400	$ 7,862	$ 19,570
Liabilities, Fair Value Disclosure, Recurring	2,100	8,400
Certificates of deposit
Financial assets:
Marketable securities	219	240
Certificates of deposit | Level 2
Financial assets:
Marketable securities	219	240
Corporate notes/bonds
Financial assets:
Marketable securities	52,962	47,673
Corporate notes/bonds | Level 1
Financial assets:
Marketable securities	52,962	47,673
U.S. government agency securities
Financial assets:
Marketable securities	991	2,402
U.S. government agency securities | Level 2
Financial assets:
Marketable securities	$ 991	$ 2,402