Financial Derivatives - Schedule of Derivative Instruments, Gain(Loss) in Statement of Financial Performance (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]
(Losses)/gains on financial derivatives and hedging activities	$ (7,578,000)	$ 4,494,000
Derivative, Notional Amount	6,628,072,000		6,691,851,000
Non-Interest Income [Member]
Derivative [Line Items]
(Losses)/gains on financial derivatives and hedging activities	(7,578,000)	4,494,000
Non-Interest Income [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	2,750,000	(3,138,000)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	2,950,000	2,653,000
Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(10,528,000)	1,841,000
Basis Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	565,189,000		404,288,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	6,600,000,000
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	200,000	5,791,000
Gain (Loss) on Components Excluded from Assessment of Interest Rate Fair Value Hedge Effectiveness	(2,900,000)	(3,000,000)
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	0	300,000
Interest Rate Swap [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(9,548,000)	2,846,000
Agency Forward [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	0		65,704,000
Agency Forward [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(852,000)	(984,000)
Treasury Futures [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	18,400,000		5,600,000
Treasury Futures [Member] | Non-Interest Income [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(128,000)	(21,000)
Zions First National Bank [Member] | Basis Swap [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	100,000	200,000
Derivative, Notional Amount	22,100,000		29,300,000
Derivative, Fair Value, Net	$ (200,000)		$ (200,000)