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

Income Tax - Components of Income Tax Benefit (Detail) (USD $)	3 Months Ended						12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2012
Investments, Owned, Federal Income Tax Note [Line Items]
Federal						$ 0			$ 0
State						0			0
Total net tax (expense) benefit	(189,000)us-gaap_IncomeTaxExpenseBenefit	(607,000)us-gaap_IncomeTaxExpenseBenefit	830,000us-gaap_IncomeTaxExpenseBenefit	(60,000)us-gaap_IncomeTaxExpenseBenefit	251,000us-gaap_IncomeTaxExpenseBenefit		(26,000)us-gaap_IncomeTaxExpenseBenefit	251,000us-gaap_IncomeTaxExpenseBenefit
TRS [Member]
Investments, Owned, Federal Income Tax Note [Line Items]
Federal							0	200,000
State								100,000
Total net tax (expense) benefit							$ 0	$ 300,000