Income taxes - Narrative (Details) - USD ($)		12 Months Ended
	Jan. 01, 2018	Jun. 30, 2019	Jun. 30, 2018		Jun. 30, 2017		May 31, 2017
Operating Loss Carryforwards [Line Items]
Provision for income taxes		$ 1,283,000	$ 1,012,000	[1]	$ 841,000	[1]
Effective tax rate (in percent)		(4.00%)	(3.00%)
Research and development tax credit carryforwards							$ 947,000
Deferred tax assets		$ 89,783,000	$ 81,932,000
Deferred tax liability		40,649,000	13,702,000
Net deferred tax assets		764,000	528,000
Increase (decrease) in valuation allowance		(19,300,000)	13,900,000		25,900,000
Decrease in gross deferred tax asset due to reduction in federal corporate tax rate	$ 18,900,000
Earnings of foreign subsidiaries that are permanently reinvested and no U.S. income taxes have been provided		9,400,000
Unrecognized deferred tax liability related to undistributed foreign earnings		364,000
Unrecognized tax benefits that if recognized would affect the annual effective tax rate		100,000	100,000		100,000
Unrecognized tax benefits - interest and penalties expense		0	15,000		17,000
Unrecognized tax benefits - interest and penalties accrued		0	$ 97,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		14,300,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credit carryforwards		11,500,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred tax assets		939,000
Deferred tax liability		175,000
Net deferred tax assets		764,000
Net operating loss carryforwards		3,500,000
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		250,200,000
Operating loss carry forwards subject to expiration		116,300,000
Operating loss carry forwards not subject to expiration		133,900,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credit carryforwards		7,000,000.0
Valuation Allowance, Operating Loss Carryforwards
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance		$ 500,000
Tax Year 2012
Operating Loss Carryforwards [Line Items]
Provision for income taxes					$ 425,000

[1] See Note 1 for a summary of adjustments.