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, 2017	Mar. 21, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	$ 34			$ 155
Predecessor
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense		$ 629	$ 89		$ 3,228
One-time Severance and Termination Benefits
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	30			142
One-time Severance and Termination Benefits | Predecessor
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense		608	$ 89		3,125
Professional Fees
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense	$ 4			$ 13
Professional Fees | Predecessor
Restructuring Cost and Reserve [Line Items]
Cost reduction initiatives expense		$ 21			$ 103