Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended			28 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017
Commitments and Contingencies (Details) [Line Items]
Rent expense	$ 1,500	$ 831	$ 1,200
Tax protection agreements, period (in years)				10 years
Terranomics Crossroads Associates, LP
Commitments and Contingencies (Details) [Line Items]
Ownership percentage (in percentage)			51.00%
Tax protection agreements, period (in years)	12 years
SARM Five Points LLC
Commitments and Contingencies (Details) [Line Items]
Ownership percentage (in percentage)			100.00%