Gain Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Deep Water Horizon Oil Spill
Gain Contingencies [Line Items]
Gain contingency	$ 2.8
Fleet Manager
Gain Contingencies [Line Items]
Gain contingency	2.8
Gain contingency, number of vessels	3
Gain contingency, percentage of gross proceeds	10.00%
Fleet Manager \| ATEL Capital Equipment Fund VII, L.P.
Gain Contingencies [Line Items]
Gain contingency	$ 1.4

The amount or range of possible amounts of gain that could be realized upon the resolution of a contingency.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 30

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant