Organization - Narrative (Detail)	9 Months Ended
Sep. 30, 2012
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Percentage of the Company's common shares owned by Annaly Capital Management, Inc.	4.38%
Company manager	Fixed Income Discount Advisory Company
Nature of relationship	FIDAC is a wholly-owned subsidiary of Annaly

This element represents a description of the nature of common ownership or management control relationships with other entities, regardless of there being transactions between the entities, when the existence of that control could result in operating results or financial position of the reporting entity significantly different from that which would have been obtained if the entities' were autonomous.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39691-107864

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Name:	us-gaap_NatureOfCommonOwnershipOrManagementControlRelationships
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration