Income taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit—beginning of period	$ 4,600	$ 3,820	$ 3,035
Increase in tax positions taken during the current period	753	825	785
Increase in tax positions taken during the prior period	0	181	0
Decrease in tax positions taken during the prior period	0	(128)	0
Decrease in tax positions due to settlements	0	(98)	0
Lapse of statute of limitations	0	0	0
Unrecognized tax benefit—end of period	$ 5,353	$ 4,600	$ 3,820