Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Impact from adoption of ASU 2018-02	[1]		$ 59
Reclassification
Increase to cost of spare parts and equipment sales		$ 700		$ 2,600
Decrease to Write-down of equipment		$ (700)		$ (2,600)

[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.