Balance sheet components - Change in deferred revenue (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2018	Jul. 01, 2017
Contract with Customer, Liability [Roll Forward]
Deferred revenue, beginning of period	$ 45,567	$ 36,160
Recognition of revenue included in beginning of period deferred revenue	(8,367)	(5,171)
Revenue deferred, net of revenue recognized on contracts in the respective period	18,594	11,817
Deferred revenue, end of period	$ 55,794	$ 42,806