Variable Interest Entities - Summary of VIEs (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 MW
Variable Interest Entity, Not Primary Beneficiary [Member] | Pilesgrove [Member] | New Jersey [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	9
Year of Initial Investment	2010
Maximum exposure to loss	$ 26,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Mesquite Solar 1 [Member] | Arizona [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	83
Power Purchase Agreement Term in Years	20 years
Year of Initial Investment	2013
Maximum exposure to loss	100,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Copper Mountain Solar 2 [Member] | Nevada [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	75
Power Purchase Agreement Term in Years	25 years
Year of Initial Investment	2013
Maximum exposure to loss	79,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Copper Mountain Solar 3 [Member] | Nevada [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	128
Power Purchase Agreement Term in Years	20 years
Year of Initial Investment	2014
Maximum exposure to loss	187,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | California Solar [Member] | California [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	55
Power Purchase Agreement Term in Years	25 years
Year of Initial Investment	2012
Maximum exposure to loss	71,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Broken Bow II [Member] | Nebraska [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	37
Power Purchase Agreement Term in Years	25 years
Year of Initial Investment	2014
Maximum exposure to loss	57,000,000
Variable Interest Entity, Primary Beneficiary [Member] | Texas Solar 4 [Member] | Texas [Member]
Variable Interest Entity [Line Items]
Generating Capacity Owned (MWs AC)	32
Power Purchase Agreement Term in Years	25 years
Year of Initial Investment	2014
Maximum exposure to loss	$ 55,000,000