Nature of operations and summary of significant accounting policies (Cost Reduction Initiatives) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Mar. 21, 2017	Sep. 30, 2017	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	$ 210	$ 34		$ 155	$ 1,034
Predecessor
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense			$ 629
One-time Severance and Termination Benefits
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	210	30		142	1,034
One-time Severance and Termination Benefits | Predecessor
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense			608
Professional Fees
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	$ 0	$ 4		$ 13	$ 0
Professional Fees | Predecessor
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense			$ 21