Hannon Armstrong Sustainable Infrastructure Capital, Inc. Annual report pursuant to Section 13 and 15(d)

Equity Method Investment in Affiliate - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2014	Oct. 20, 2014
Schedule of Equity Method Investments [Line Items]
Loss from equity method investment in affiliate	$ 448,000	$ 1,284,000
Strong Upwind Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Project investment amount					144,000,000	144,000,000
HA EnergySource [Member]
Schedule of Equity Method Investments [Line Items]
Capital commitment, approved				3,400,000
Loss from equity method investment in affiliate	500,000	1,300,000
Cash distributions of excess financing proceeds		12,600,000
Deemed distributions		1,700,000
Investments in affiliates		800,000		0
Management services to EnergySource	$ 100,000	$ 8,800,000	$ 0	$ 500,000