Financial Derivatives - Schedule of Derivative Instruments, Gain(Loss) in Statement of Financial Performance (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Derivative [Line Items]
(Losses)/gains on financial derivatives and hedging activities	$ (5,698,000)	$ 14,983,000	$ (13,276,000)	$ 19,477,000
Non-Interest Income [Member]
Derivative [Line Items]
(Losses)/gains on financial derivatives and hedging activities	(5,698,000)	14,983,000	(13,276,000)	19,477,000
Non-Interest Income [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	3,818,000	(14,729,000)	6,568,000	(17,867,000)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	3,019,000	2,806,000	5,969,000	5,459,000
Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(8,717,000)	12,177,000	(19,245,000)	14,018,000
Interest Rate Swap [Member] | Non-Interest Income [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(799,000)	17,535,000	(599,000)	23,326,000
Gain (Loss) on Components Excluded from Assessment of Interest Rate Fair Value Hedge Effectiveness	(2,900,000)	(3,000,000)	(5,900,000)	(6,000,000)
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	100,000	200,000	100,000	500,000
Interest Rate Swap [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(8,126,000)	10,913,000	(17,674,000)	13,759,000
Agency Forward [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(235,000)	1,076,000	(1,087,000)	92,000
Treasury Futures [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ (356,000)	$ 188,000	$ (484,000)	$ 167,000