Fresh start accounting (Reorganization items) (Details) - USD ($) $ in Thousands		3 Months Ended					9 Months Ended	12 Months Ended
	Mar. 21, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 21, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Fresh-Start Adjustment [Line Items]
Loss (gain) on the settlement of liabilities subject to compromise							$ 0	$ 48
Fresh start accounting adjustments							0	0
Professional fees							3,091	2,344
Claims for non-performance of executory contract							0	0
Rejection of employment contracts							0	0
Write off unamortized issuance costs on Prior Credit Facility							0	0
Total reorganization items		$ 543	$ 858	$ 1,070	$ 620		$ 3,091	$ 2,392
Predecessor
Fresh-Start Adjustment [Line Items]
Loss (gain) on the settlement of liabilities subject to compromise	$ (372,093)					$ (372,093)			$ 0
Fresh start accounting adjustments						(641,684)			0
Professional fees						18,790			15,484
Claims for non-performance of executory contract						0			1,236
Rejection of employment contracts						4,573			0
Write off unamortized issuance costs on Prior Credit Facility						1,687			0
Total reorganization items						$ (988,727)			$ 16,720