Nature of operations and summary of significant accounting policies (Cost Reduction Initiatives) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 21, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	$ 629	$ 691	$ 0	$ 1,034
One-time severance and termination benefits
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	608	678		1,034
Professional fees
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	$ 21	$ 13		$ 0