Cash, cash equivalents and short-term investments - Summary of cash, cash equivalents and short-term investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Cash	$ 23,010	$ 20,323
Total cash equivalents	5,303	195
Total cash and cash equivalents	28,313	20,518	$ 19,278
Debt securities
Amortized Cost	69,250
Estimated Fair Value	70,505
Short-term investments
Amortized Cost	69,250	88,745
Unrealized Gains	1,256	1,570
Unrealized Losses	(1)	0
Estimated Fair Value	70,505	90,315
Cash, cash equivalents and short-term investments
Amortized Cost	97,563	109,263
Unrealized Gains	1,256	1,570
Unrealized Losses	(1)	0
Estimated Fair Value	98,818	110,833
U.S. treasury securities
Debt securities
Amortized Cost	1,532	3,712
Unrealized Gains	27	41
Unrealized Losses	0	0
Estimated Fair Value	1,559	3,753
U.S. agency securities
Debt securities
Amortized Cost	3,188	5,004
Unrealized Gains	44	54
Unrealized Losses	0	0
Estimated Fair Value	3,232	5,058
Short-term investments
Estimated Fair Value	3,232	5,058
Asset-backed securities
Debt securities
Amortized Cost	16,599	20,392
Unrealized Gains	352	434
Unrealized Losses	0	0
Estimated Fair Value	16,951	20,826
Short-term investments
Estimated Fair Value	16,951	20,826
Municipal securities
Debt securities
Amortized Cost	6,280	9,464
Unrealized Gains	83	78
Unrealized Losses	0	0
Estimated Fair Value	6,363	9,542
Short-term investments
Estimated Fair Value	6,363	9,542
Corporate bonds
Debt securities
Amortized Cost	41,651	50,173
Unrealized Gains	750	963
Unrealized Losses	(1)	0
Estimated Fair Value	42,400	51,136
Short-term investments
Estimated Fair Value	42,400	51,136
Money market mutual funds
Debt Securities, Available-for-sale [Line Items]
Total cash equivalents	$ 5,303	$ 195