Revenue Recognition - Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenue	$ 21,189	$ 19,240
Product, accessories and parts
Disaggregation of Revenue [Line Items]
Total revenue	17,085	15,491
Microturbine products
Disaggregation of Revenue [Line Items]
Total revenue	13,633
Accessories and parts
Disaggregation of Revenue [Line Items]
Total revenue	3,452
Service
Disaggregation of Revenue [Line Items]
Total revenue	4,104	$ 3,749
Total North America
Disaggregation of Revenue [Line Items]
Total revenue	11,599
United States
Disaggregation of Revenue [Line Items]
Total revenue	10,874
Mexico
Disaggregation of Revenue [Line Items]
Total revenue	609
All other North America
Disaggregation of Revenue [Line Items]
Total revenue	116
Europe
Disaggregation of Revenue [Line Items]
Total revenue	4,873
Columbia
Disaggregation of Revenue [Line Items]
Total revenue	2,616
Asia
Disaggregation of Revenue [Line Items]
Total revenue	854
Australia
Disaggregation of Revenue [Line Items]
Total revenue	853
All other
Disaggregation of Revenue [Line Items]
Total revenue	$ 394