Financial Derivatives - Derivative Gain/(Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	$ (31,292)	$ (17,806)	$ (24,892)	$ (13,801)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(31,292)	(17,806)	(24,892)	(13,801)
Interest Rate Swap | Non-Interest Income | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(30,187)	(16,451)	(23,882)	(11,721)
Agency Forwards | Non-Interest Income | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(809)	(1,153)	(605)	(2,001)
Treasury Futures | Non-Interest Income | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	(295)	(211)	(329)	(26)
Credit Default Swaps | Non-Interest Income | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Losses on financial derivatives	$ (1)	$ 9	$ (76)	$ (53)