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

Financing Receivables and Investments - Summary of Anticipated Maturity Dates of Financing Receivables and Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2012
Receivables [Abstract]
Financing Receivables, payment due total	$ 358,871
Financing Receivables, payment due in less than 1 year	924
Financing Receivables, payment due in 1-5 years	114,628
Financing Receivables, payment due in 5-10 years	7,470
Financing Receivables, payment due in more than 10 years	235,849
Investments, payment due total	91,964
Investments, payment due in less than 1 year
Investments, payment due in 1-5 years	15,101
Investments, payment due in 5-10 years
Investments, payment due in more than 10 years	$ 76,863