Transactions With Related Parties Transactions With Related Parties (Schedule of Amount Received in Public and Private Partnerships) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Well supervision and other fees	$ 172	$ 254	$ 423
General and administrative expense reimbursement	$ 0	$ 6	$ 18