Revenue from contracts with customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended			9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 18, 2018	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Refund period					30 days	14 days
Discounts to customers	$ 1	$ 9	$ 2	$ 17