Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2016
Income taxes [Abstract]
Income tax provision	$ 178	$ 459	$ 459
Effective tax rate	20.70%	32.70%	32.70%
Total gross unrecognized tax benefits that would impact the effective rate	$ 104
Previously unrecognized tax benefit recognized	28
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 20