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Stockholders' equity - Narrative - Stock Repurchase Program and Stock Plans (Details) - USD ($)	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018	Feb. 28, 2019
Equity, Class of Treasury Stock [Line Items]
Authorized repurchase amount				$ 20,000,000.0
Payments for stock repurchases	$ 9,353,000	$ 1,303,000	$ 0
Number of shares repurchased (in shares)	1,692,207	221,333
Average purchase price per share (in dollars per share)	$ 5.53	$ 5.89
Share repurchase program, remaining authorized stock repurchases, amount	$ 9,300,000
Stock repurchases	9,353,000	$ 1,303,000
Additional Paid-in Capital
Equity, Class of Treasury Stock [Line Items]
Stock repurchases	5,790,000	714,000
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Stock repurchases	$ 3,561,000	$ 589,000
Stock options
Equity, Class of Treasury Stock [Line Items]
Award vesting period (in years)	4 years
Option expiration period	10 years
Restricted stock units \| Minimum
Equity, Class of Treasury Stock [Line Items]
Award vesting period (in years)	3 years
Restricted stock units \| Maximum
Equity, Class of Treasury Stock [Line Items]
Award vesting period (in years)	4 years