Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Impact from adoption of ASU 2018-02	[1]	$ 59
Reclassification
Increase to Cost of spare parts and equipment sales		900	$ 900
Decrease to Write-down of equipment		$ (900)

[1] Reflects the stranded tax effects from change in tax rate as a result of the early adoption of ASU 2018-02 which has been reclassified to retained earnings.