Revenue Recognition - Disaggregation of Revenue (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2018 USD ($)
Grid
Disaggregation of Revenue [Line Items]
Revenue	$ 8,929
Grid | Americas
Disaggregation of Revenue [Line Items]
Revenue	7,496
Grid | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	808
Grid | EMEA
Disaggregation of Revenue [Line Items]
Revenue	625
Grid | Equipment and systems
Disaggregation of Revenue [Line Items]
Revenue	7,462
Grid | Services and technology development
Disaggregation of Revenue [Line Items]
Revenue	1,467
Wind
Disaggregation of Revenue [Line Items]
Revenue	3,678
Wind | Americas
Disaggregation of Revenue [Line Items]
Revenue	23
Wind | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	3,595
Wind | EMEA
Disaggregation of Revenue [Line Items]
Revenue	60
Wind | Equipment and systems
Disaggregation of Revenue [Line Items]
Revenue	3,492
Wind | Services and technology development
Disaggregation of Revenue [Line Items]
Revenue	$ 186