Summary of Offsetting Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives instrument
Gross fair value of recognized assets	$ 32,690	$ 26,647
Gross fair value not offset in balance sheets
Financial Instruments	(32,468)	(26,647)
Net fair value	222
Short-term reverse repurchase agreement
Gross fair value of recognized assets	750,000	4,138
Gross fair value not offset in balance sheets
Financial Instruments	(750,000)	(4,138)
Total financial instrument
Gross fair value of recognized assets	782,690	30,785
Gross fair value not offset in balance sheets
Financial Instruments	(782,468)	(30,785)
Net fair value	222
Derivatives instrument
Gross fair value of recognized liabilities	113,564	87,093
Gross fair value not offset in balance sheets
Financial Instruments	(32,468)	(26,647)
Cash collateral pledged	(80,573)	(54,400)
Net fair value	$ 523	$ 6,046

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Amount of derivative assets, securities purchased under agreements to resell and securities borrowed offset against an obligation to return collateral under a master netting arrangement. Includes assets not subject to a master netting arrangement and not elected to be offset.

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No definition available.

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Amount of obligation to return financial instruments collateral under master netting arrangements that have not been offset against derivative assets, securities purchased under agreements to resell and securities borrowed.

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No definition available.

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Amount, before effects of master netting arrangements, of derivative assets, securities purchased under agreements to resell and securities borrowed.

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Amount of obligation to return financial instruments collateral under master netting arrangements that has not been offset against derivative assets.

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Amount of right to receive financial instruments collateral under master netting arrangements that have not been offset against derivative liabilities.

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No definition available.

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Fair value of derivative asset other than other forward contracts, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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No definition available.

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Fair value of derivative liability except other forward contracts, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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No definition available.

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Amount of obligation to return financial securities collateral under master netting arrangements that have not been offset against securities purchased under agreement to resell.

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Amount, before effects of master netting arrangements, of funds outstanding loaned in the form of a security resale agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price.

+ References

No definition available.

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The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

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The amount as of the balance sheet date of the fair value of derivative assets that in accordance with the entity's accounting policy was offset against an obligation to return cash collateral under a master netting arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10B

-Subparagraph b

-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.

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The amount as of the balance sheet date of the fair value of derivative liabilities that in accordance with the entity's accounting policy were offset against the right to reclaim cash collateral under a master netting arrangement.

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