Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2016		Mar. 31, 2016	Dec. 31, 2015		Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014
Assets: [Abstract]
Trading securities	$ 211,622			$ 122,404		$ 158,209
Available for sale securities	8,830,689			9,042,733		9,000,117
Fair value option securities	263,265			444,217		436,324
Mortgage servicing rights	190,747		$ 196,055	218,605		198,694		$ 175,051	$ 171,976
Derviative contracts, net of cash collateral, Assets, Fair value	883,673			586,270		630,435
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	719,159			581,701		620,277
U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	18,909			61,295		40,212
U.S. government agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	122,306			10,989		23,090
Available for sale securities	5,700,268	[1]		5,898,351		6,339,449
Fair value option securities	237,959			444,217		436,324
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	52,721			31,901		62,801
Available for sale securities	50,262			56,817		61,624
Other trading securities [Member]
Assets: [Abstract]
Trading securities	17,686			18,219		32,106
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,004			995		1,000
Fair value option securities	25,306			0		0
Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	126,313			139,118		154,150
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,911,946			2,905,796		2,401,364
Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	4,151			4,151		4,150
Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	17,931			19,672		19,648
Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	18,814			17,833		18,732
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	211,622			122,404		158,209
Available for sale securities	8,830,689			9,042,733		9,000,117
Fair value option securities	263,265			444,217		436,324
Residential mortgage loans held for sale	430,728			308,439		502,571
Mortgage servicing rights	190,747	[2]		218,605	[3]	198,694	[4]
Derviative contracts, net of cash collateral, Assets, Fair value	883,673	[5]		586,270	[6]	630,435	[7]
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	719,159	[5]		581,701	[6]	620,277	[7]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	18,909			61,295		40,212
Fair Value, Measurements, Recurring [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	122,306			10,989		23,090
Available for sale securities	5,700,268			5,898,351		6,339,449
Fair value option securities	237,959			444,217		436,324
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	52,721			31,901		62,801
Available for sale securities	50,262			56,817		61,624
Fair Value, Measurements, Recurring [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	17,686			18,219		32,106
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,004			995		1,000
Fair value option securities	25,306			0		0
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	126,313			139,118		154,150
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,911,946			2,905,796		2,401,364
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	4,151			4,151		4,150
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	17,931			19,672		19,648
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	18,814			17,833		18,732
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	4,789			4,260		5,216
Fair value option securities	25,306			0		0
Residential mortgage loans held for sale	0			0		0
Mortgage servicing rights	0			0		0
Derviative contracts, net of cash collateral, Assets, Fair value	7,246			38,530		11,484
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	4,808			0		1,080
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	0			0		0
Fair value option securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,004			995		1,000
Fair value option securities	25,306			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	3,785			3,265		4,216
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	211,622			122,404		158,209
Available for sale securities	8,812,149			9,024,712		8,981,134
Fair value option securities	237,959			444,217		436,324
Residential mortgage loans held for sale	420,979			300,565		494,598
Mortgage servicing rights	0			0		0
Derviative contracts, net of cash collateral, Assets, Fair value	876,427			547,740		618,951
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	714,351			581,701		619,197
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	18,909			61,295		40,212
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	122,306			10,989		23,090
Available for sale securities	5,700,268			5,898,351		6,339,449
Fair value option securities	237,959			444,217		436,324
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	52,721			31,901		62,801
Available for sale securities	40,662			47,207		52,007
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	17,686			18,219		32,106
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair value option securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	126,313			139,118		154,150
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,911,946			2,905,796		2,401,364
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	17,931			19,672		19,648
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	15,029			14,568		14,516
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	13,751			13,761		13,767
Fair value option securities	0			0		0
Residential mortgage loans held for sale	9,749			7,874		7,973
Mortgage servicing rights	190,747			218,605		198,694
Derviative contracts, net of cash collateral, Assets, Fair value	0			0		0
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	0			0		0
Fair value option securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	9,600			9,610		9,617
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair value option securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	4,151			4,151		4,150
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	$ 0			$ 0		$ 0

[1] U.S. government and government sponsored enterprises are not rated by the nationally-recognized rating agencies as these securities are guaranteed by agencies of the U.S. government or government-sponsored enterprises.

[2] A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 6, Mortgage Banking Activities.

[3] A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 6, Mortgage Banking Activities.

[4] A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 6, Mortgage Banking Activities.

[5] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in asset positions that were valued based on quoted prices in active markets for identical instruments (Level 1) are primarily exchange-traded energy and agricultural derivative contacts, net of cash margin. Derivative contacts in liability positions that were valued using quoted prices in active markets for identical instruments are exchange-traded interest rate and energy derivative contracts, net of cash margin.

[6] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded energy derivative contacts, net of cash margin. Derivative contracts in liability positions that were valued using quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and agricultural derivative contracts, net of cash margin.

[7] See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded energy derivative contacts, net of cash margin. Derivative contracts in liability positions that were valued using quoted prices in active markets for identical instruments (Level 1) were exchange-traded agricultural derivative contracts.