Variable Interest Entities (Narrative) (Detail)	6 Months Ended
Jun. 30, 2012
Percentage of common equity of trusts	100.00%

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 5A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759159-111685

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration