Restructuring Charges (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Severance expense	$ 41	$ 662
Severance [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charge			$ 3,549
Asset Retirements [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charge			32,309
Pre-contract Costs [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charge			6,441
Closeout Costs [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charge			$ 4,194