Financial Derivatives - Derivative Gain/(Loss) (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives instruments and hedging activity net pretax	$ 1,558,000		$ (68,567,000)		$ (23,334,000)		$ (82,368,000)
Non-Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives instruments and hedging activity net pretax	1,558,000		(68,567,000)		(23,334,000)		(82,368,000)
Non-Interest Income [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Items	8,378,000		0		8,378,000		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings	3,236,000	[1]	0	[1]	3,236,000	[1]	0	[1]
Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities	(1,678,000)		(68,567,000)		(26,570,000)		(82,368,000)
Interest Rate Swap, Pay Fixed Non-Callable [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Hedge Assets	0				0
Fair Value Hedge Liabilities	63,496,000				63,496,000
Interest Rate Swap | Non-Interest Income [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(5,142,000)		0		(5,142,000)		0
Gain (Loss) from Components Excluded from Assessment of Cash Flow Hedge Effectiveness, Net	3,000,000				3,000,000
Derivative, Net Hedge Ineffectiveness Gain (Loss)	200,000				200,000
Interest Rate Swap | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities	(1,970,000)		(65,136,000)		(25,853,000)		(76,857,000)
Agency Forward [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities	452,000		(3,052,000)		(153,000)		(5,053,000)
Treasury Futures | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities	(142,000)		(512,000)		(471,000)		(538,000)
Credit Default Swaps | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities	$ (18,000)		$ 133,000		$ (93,000)		$ 80,000

[1] Includes gains of $3.0 million that are excluded from the assessment of hedge effectiveness and gains of $0.2 million due to hedge ineffectiveness for the three and nine months ended September 30, 2012.