Summary of Significant Accounting Policies - PPE Useful Lives (Details)	6 Months Ended
	Sep. 30, 2016
Land and land improvements | Minimum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	10 years
Land and land improvements | Maximum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	15 years
Buildings and building improvements | Minimum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	3 years
Buildings and building improvements | Maximum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	39 years
Furniture, fixtures and office equipment | Minimum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	2 years
Furniture, fixtures and office equipment | Maximum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	10 years
Leasehold improvements
Depreciation using the straight-line method
Property, plant and equipment estimated useful life	Shorter of asset life or life of lease
Equipment leased to customers under Power Purchase Agreements
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	20 years
Plant equipment | Minimum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	3 years
Plant equipment | Maximum
Depreciation using the straight-line method
Property, plant and equipment, useful life (years)	10 years