Fair Value Measurements - Valuations (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)		$ 1,907
Wells Project [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Finite-Lived Intangible Assets, Net	$ 4,302
Impairment of Intangible Assets (Excluding Goodwill)	1,907
Wells Project [Member] | Carrying Amount
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Finite-lived Intangible Assets, Fair Value Disclosure	$ 2,395