Financial Derivatives Narrative (Details) (USD $)								3 Months Ended		6 Months Ended															6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended									3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 Excluding netting [Member]	Jun. 30, 2013 Uncollateralized [Member]	Dec. 31, 2012 Uncollateralized [Member]	Jun. 30, 2013 Cash [Member]	Dec. 31, 2012 Cash [Member]	Jun. 30, 2013 Zions First National Bank [Member] Basis Swap [Member]	Jun. 30, 2012 Zions First National Bank [Member] Basis Swap [Member]	Jun. 30, 2013 Zions First National Bank [Member] Basis Swap [Member]	Jun. 30, 2012 Zions First National Bank [Member] Basis Swap [Member]	Dec. 31, 2012 Zions First National Bank [Member] Basis Swap [Member]	Jun. 30, 2013 Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Dec. 31, 2012 Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Non-Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Non-Callable [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member] Basis Swap [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Basis Swap [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Callable [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Swap, Receive Fixed Callable [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Jun. 30, 2013 Not Designated as Hedging Instrument [Member] Treasury Futures [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Treasury Futures [Member]	Jun. 30, 2013 Dedesignated hedge [Member]	Jun. 30, 2013 Dedesignated hedge [Member] Interest Rate Swap, Pay Fixed Non-Callable [Member]	Jun. 30, 2013 Including accrued interest [Member] Excluding netting [Member]	Dec. 31, 2012 Including accrued interest [Member] Excluding netting [Member]	Jun. 30, 2013 Including accrued interest [Member] Netting [Member]	Dec. 31, 2012 Including accrued interest [Member] Netting [Member]	Jun. 30, 2013 Including accrued interest [Member] Counterparty level [Member] Netting [Member]	Dec. 31, 2012 Including accrued interest [Member] Counterparty level [Member] Netting [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Agency Forward [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Treasury Futures [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Treasury Futures [Member]	Jun. 30, 2013 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Treasury Futures [Member]	Jun. 30, 2012 Non-Interest Income [Member] Not Designated as Hedging Instrument [Member] Treasury Futures [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held																													1
Notional Amount of Interest Rate Fair Value Hedge Derivatives													$ 900,000,000	$ 950,000,000																$ 50,000,000
Fair Value Hedge Assets													0	0
Fair Value Hedge Liabilities													35,202,000	58,758,000
Derivative Liability, Fair Value, Gross Liability	(99,063,000)	(150,682,000)															(834,000)	(211,000)	(61,043,000)	(91,205,000)	(453,000)	(784,000)	(1,933,000)	(238,000)	0	(58,000)	(30,000)	(12,000)			(116,000,000)	(168,000,000)			(92,700,000)	(135,800,000)
Obligation to Return Securities Received as Collateral						1,358,000	1,650,000
Derivative Assets	21,806,000	29,523,000
Derivative, Weighted-Average Forward Price																									$ 97.38	$ 101.22	$ 126.23	$ 129.77
Derivative, Weighted-Average Pay Rate													2.25%				0.32%	0.33%	4.62%	4.83%	0.42%	0.43%	0.13%	0.15%
Credit exposure to interest rate swap counterparties			37,100,000	2,300,000	800,000																										28,300,000		3,600,000	2,400,000
Collateral Already Posted, Aggregate Fair Value						20,279,000	60,311,000
Additional Collateral, Aggregate Fair Value	72,400,000	75,500,000
Derivative, Notional Amount	6,731,092,000	6,815,268,000						40,200,000		40,200,000		49,300,000					4,283,440,000	4,135,149,000	799,926,000	805,622,000	450,223,000	609,262,000	245,000,000	245,000,000	43,603,000	59,035,000	8,900,000	11,200,000
Derivative, Fair Value, Net								(400,000)		(400,000)		(700,000)
Gain (Loss) on Derivative Instruments, Net, Pretax								100,000	300,000	300,000	400,000																										12,177,000	(31,292,000)	14,018,000	(24,892,000)	10,913,000	(30,187,000)	13,759,000	(23,882,000)	1,076,000	(809,000)	92,000	(605,000)	188,000	(295,000)	167,000	(329,000)
Derivative, Weighted-Average Receive Rate													0.27%				0.80%	0.85%	0.27%	0.32%	0.30%	0.36%	0.52%	0.55%
Financial derivatives, at fair value	23,164,000	31,173,000															19,910,000	30,338,000	2,951,000	357,000	328,000	499,000	0	6,000	132,000	0	0	0
Derivative Credit Risk Valuation Adjustment, Derivative Assets															(157,000)	(27,000)
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities															(432,000)	(584,000)
Derivative Liabilities	$ (78,784,000)	$ (90,371,000)