Project Assets - Additional Information (Detail)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2015 USD ($) MWh	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 18, 2014 USD ($)
Schedule of Project Assets (Details) [Line Items]
Project assets		$ 107,354,000	$ 73,930,000
Calwaii [Member]
Schedule of Project Assets (Details) [Line Items]
Project asset cost held for development		28,646,000	23,943,000
Deferred Revenue				$ 5,850,000
Mauka Makai FIT LLC [Member]
Schedule of Project Assets (Details) [Line Items]
Percentage of Membership Interest Acquired	100.00%
Payments to Acquire Productive Assets	$ 4,179,000
Power Generating Capacity (in Megawatt-hours) | MWh	4.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		4,179,000
UNITED STATES
Schedule of Project Assets (Details) [Line Items]
Project assets		53,971,000	48,520,000
UNITED KINGDOM
Schedule of Project Assets (Details) [Line Items]
Project assets		44,912,000	14,000,000
JAPAN
Schedule of Project Assets (Details) [Line Items]
Project assets		14,872,000	12,826,000
CHINA
Schedule of Project Assets (Details) [Line Items]
Project assets		25,613,000	19,849,000
Mountain Creek Project [Member]
Schedule of Project Assets (Details) [Line Items]
Carrying amount of net of impairment		17,864,000	17,864,000
Impairment on project		2,055,000	2,055,000
Disposal Group, Including Discontinued Operation, Consideration			17,864,000
Loss on Contracts			$ 2,055,000
Disposal Group, Including Discontinued Operation, Revenue		0
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)		$ 0