Income taxes (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Operating Loss Carryforwards [Line Items]
Provision (benefit) for income taxes		$ 26,000	$ 537,000	$ 281,000	$ 142,000
Effective tax rate (percentage)					1.00%
Unrecognized tax benefit		3,400,000		3,400,000		$ 3,000,000
Unrecognized tax benefits that would affect effective tax rate		98,000		98,000		124,000
Interest and penalties related to unrecognized tax positions accrued		89,000		$ 89,000		91,000
Valuation allowance						$ 50,100,000
Decrease in gross deferred tax asset due to reduction in federal corporate tax rate		$ 18,800,000
State and Local Jurisdiction | New York State Division of Taxation and Finance | Tax Year 2010 - Tax Year 2012
Operating Loss Carryforwards [Line Items]
Provision (benefit) for income taxes	$ 1,000,000