Balance Sheet Details (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Apr. 01, 2017	Sep. 30, 2017
Inventory, Net [Abstract]
Purchased parts and assemblies	$ 137,511		$ 114,285
Work-in-process	189,461		159,784
Finished goods	165,714		140,738
Total inventories	492,686		414,807
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid and refundable income taxes	33,478		28,712
Other taxes receivable	20,577		15,327
Prepaid expenses and other assets	31,391		26,229
Total prepaid expenses and other assets	85,446		70,268
Other Assets, Noncurrent Disclosure [Abstract]
Assets related to deferred compensation arrangements	33,740		31,008
Deferred tax assets	85,034		82,691
Other assets	8,079		12,942
Total other assets	126,853		126,641
Other Liabilities, Current [Abstract]
Accrued payroll and benefits	68,203		72,327
Deferred revenue	34,608		65,237
Warranty reserve	37,479		36,149
Accrued expenses and other	35,050		34,215
Current liabilities held for sale (see Note 19)	732		7,021
Customer deposits	19,770		20,052
Total other current liabilities	195,842		235,001
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Beginning balance	36,149	$ 15,949
Additions related to current period sales	24,290	16,135
Warranty costs incurred in the current period	(24,212)	(15,105)
Accruals resulting from acquisitions	179	14,314
Adjustments to accruals related to foreign exchange and other	1,073	(507)
Ending balance	37,479	$ 30,786
Other Liabilities, Noncurrent [Abstract]
Long-term taxes payable	60,259		35,866
Deferred compensation	37,137		34,160
Deferred tax liabilities	45,360		45,373
Deferred revenue	4,724		4,765
Asset retirement obligations liability	5,078		5,382
Defined benefit plan liabilities	41,719		39,454
Other long-term liabilities	1,006		1,390
Total other long-term liabilities	$ 195,283		$ 166,390