Fresh start accounting (Reorganization Items) (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 21, 2017	Mar. 21, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Fresh Start Accounting [Abstract]
Loss (gain) on the settlement of liabilities subject to compromise	$ (372,093)	$ (372,093)	$ 0	$ 0	$ 48
Fresh start accounting adjustments		(641,684)	0	0	0
Professional fees		18,790	3,091	1,753	2,344
Rejection of employment contracts		4,573	0	0	0
Write off unamortized issuance costs on Prior Credit Facility		1,687	0	0	0
Total reorganization items		$ (988,727)	$ 3,091	$ 1,753	$ 2,392