Receivables (Allowance for doubtful accounts) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	11 Months Ended	12 Months Ended
	Feb. 08, 2018	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Charged to expense			$ 22,438
Predecessor
Allowance for Doubtful Accounts Receivable [Roll Forward]
Charged to expense	$ 0			$ 0	$ 0
Trade receivables
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period		$ 95	415
Charged to expense			25
Deductions			(345)
Balance at end of period	415		95
Trade receivables | Predecessor
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period	415		415	490	1,030
Charged to expense	0			(69)	243
Deductions	0			(6)	(783)
Balance at end of period	415			415	490
Related party receivables
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period		22,438	0
Charged to expense			22,438
Deductions			0
Balance at end of period	0		22,438
Related party receivables | Predecessor
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period	0		0	0	0
Charged to expense	0			0	0
Deductions	0			0	0
Balance at end of period	$ 0			$ 0	$ 0
High Mesa
Allowance for Doubtful Accounts Receivable [Roll Forward]
Accounts receivable, related party			23,400
Subsequent Event | High Mesa
Allowance for Doubtful Accounts Receivable [Roll Forward]
Accounts receivable, related party		22,400
Payment received		1,000
General and Administrative Expense | High Mesa
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period		$ 22,400
Balance at end of period			$ 22,400