Derivative Financial Instruments - Narrative (Details)	3 Months Ended
Mar. 31, 2013
Derivitive Financial Instruments [Line Items]
Type of Derivative Instrument	Eurodollar futures contracts
Underlying Risk	interest rate risk

Description of the risk underlying the derivative not designated as a hedging instrument. For example, interest rate risk, currency exchange risk, credit risk, or price risk.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41641-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579240-113959

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