Cash, cash equivalents and short-term investments - Summary of cost and estimated fair value of short-term investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Due within one year	$ 37,114
Due between one and two years	19,568
Due between two and three years	7,223
Amortized Cost	63,905
Due within one year	36,953
Due between one and two years	19,377
Due between two and three years	7,214
Total	$ 63,544	$ 67,829