Commitments and contingencies (Details) $ in Millions		9 Months Ended
	Mar. 10, 2017 patent	Jun. 30, 2018 USD ($)
Long-term Purchase Commitment [Line Items]
Purchase agreement obligation, term, non-cancelable		28 days
Implicit, LLC
Long-term Purchase Commitment [Line Items]
Loss contingency, patents allegedly infringed upon, number | patent	2
Inventories
Long-term Purchase Commitment [Line Items]
Purchase agreement obligation, term, cancelable		29 days
Purchase agreement obligation		$ 40.9
Purchase agreement obligation, remainder of 2018		38.9
Purchase agreement obligation, 2019		$ 2.0