Offsetting Assets and Liabilities (Details) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Offsetting of Assets and Liabilities [Line Items]
Securities Collateral realting to Repurchase and Reverse Repurchase Agreements	$ 1,480,000,000		$ 1,050,000,000
Reverse Repurchase Agreements	(1,287,992,000)		(905,718,000)
Financial derivatives-liabilities at fair value-	(18,543,000)		(15,212,000)
Financial derivatives-assets at fair value-	46,977,000		48,504,000
Derivative Asset, Fair Value, Net	28,434,000	[1]	33,292,000	[1]
Fair value	41,188,000	[1]	13,650,000	[1]
Net Value, Repurchase and Reverse Repurchase Agreements	(1,246,804,000)	[1]	(892,068,000)	[1]
Collateral for offsetting relating to Repurchase and Reverse Repurchase Agreements	1,229,994,000	[2],[3]	887,940,000	[2],[3]
Securities Collateral on Derivatives	0	[2],[3]	0	[2],[3]
Cash collateral (Received) Pledged for Derivatives	(6,150,000)	[2]	(13,188,000)	[2]
Cash Collateral (Received) Pledged, Reverse and Reverse Repurchase Agreements	16,810,000	[2]	4,128,000	[2]
Net Amount, Derivatives	22,284,000		20,104,000
Net Amount, Repurchase and Reverse Repurchase Agreements	0		0
Financial Derivatives - Assets [Member]
Offsetting of Assets and Liabilities [Line Items]
Financial derivatives-assets at fair value-	46,977,000	[1],[4]	48,504,000	[1],[4]
Financial Derivatives - Liabilities [Member]
Offsetting of Assets and Liabilities [Line Items]
Financial derivatives-liabilities at fair value-	(18,543,000)	[1],[4]	(15,212,000)	[1],[4]
Securities Sold under Agreements to Repurchase [Member]
Offsetting of Assets and Liabilities [Line Items]
Reverse Repurchase Agreements	$ (1,287,992,000)	[1]	$ (905,718,000)	[1]

[1] In the Company’s Consolidated Statement of Assets, Liabilities, and Equity, all balances associated with the repurchase agreements, reverse repurchase agreements, and derivatives transactions are presented on a gross basis.

[2] As collateral is called or posted per counterparty it is generally called or posted across all positions with each respective counterparty.

[3] Amounts disclosed in the Financial Instruments column of the table represent collateral that is available to be offset against balances associated with repurchase and reverse repurchase agreements. For the purposes of the table above, total financial instruments and cash collateral (received) pledged can not exceed the gross amount of assets and (liabilities) as presented above. Therefore we have reduced the amount of financial instruments related to our repurchase and reverse repurchase agreements in the table above. Total financial instruments for June 30, 2013 and December 31, 2012 were $1.48 billion and $1.05 billion, respectively.

[4] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.