Offsetting Assets and Liabilities Offsettting Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Offsetting Liabilities [Line Items]
Derivative liabilities, fair value, gross liability	$ 35,898		$ 6,681
Derivative liabilities, fair value, gross amount offset in balance sheet	0		0
Derivative liabilities, fair value, amount not offset against collateral	35,898		6,681
Derivative, Collateral, Right to Reclaim Securities	(2,494)	[1]	(1,299)	[1]
Derivative, Collateral, Right to Reclaim Cash	(32,994)	[1]	(5,382)	[1]
Derivative liabilities, fair value, amount offset against collateral	410		0
Repurchase agreements, gross liability	3,013,110		3,580,754
Repurchase agreements, gross amount offset in balance sheet	0		0
Repurchase agreements, amount not offset against collateral	3,013,110		3,580,754
Repurchase agreements, Collateral, Right to Reclaim Securities	(3,013,110)	[1]	(3,580,754)	[1]
Repurchase agreements, Collateral, Right to Reclaim Cash	0	[1]	0	[1]
Repurchase agreements, amount offset against collateral	0		0
Total gross liabilities	3,049,008		3,587,435
Total gross liabilities, gross amount offset in balance sheet	0		0
Total liabilities, amount not offset against collateral	3,049,008		3,587,435
Total liabilities, Collateral, Right to Reclaim Securities	(3,015,604)	[1]	(3,582,053)	[1]
Total liabilities, Collateral, Right to Reclaim Cash	(32,994)	[1]	(5,382)	[1]
Total liabilities, amount offset against collateral	$ 410		$ 0

[1] 1) Amount disclosed for collateral received by or posted to the same counterparty include cash and the fair value of MBS up to and not exceeding the net amount of the asset or liability presented in the balance sheet. The fair value of the actual collateral received by or posted to the same counterparty may exceed the amounts presented.