Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015		Dec. 31, 2014
Assets: [Abstract]
Trading securities	$ 279,539		$ 122,404		$ 118,044
Available for sale securities	8,886,036		9,042,733		9,158,175
Fair value option securities	418,887		444,217		434,077
Mortgage servicing rights	196,055		218,605		175,051		$ 171,976
Derviative contracts, net of cash collateral, Assets, Fair value	790,146		586,270		462,386
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	705,578		581,701		419,351
U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	59,733		61,295		26,283
U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	146,896		10,989		17,179
Available for sale securities	5,716,525	[1]	5,898,351		6,717,569
Fair value option securities	418,887		444,217		434,077
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	58,797		31,901		54,164
Available for sale securities	51,308		56,817		60,818
Other trading securities [Member]
Assets: [Abstract]
Trading securities	14,113		18,219		20,418
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,003		995		1,001
Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	133,030		139,118		160,031
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,942,404		2,905,796		2,164,842
Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	4,151		4,151		9,155
Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	19,575		19,672		24,983
Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	18,040		17,833		19,776
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	279,539		122,404		118,044
Available for sale securities	8,886,036		9,042,733		9,158,175
Residential mortgage loans held for sale	332,040		308,439		513,196
Mortgage servicing rights	196,055	[2]	218,605	[3]	175,051	[4]
Derviative contracts, net of cash collateral, Assets, Fair value	790,146	[5]	586,270	[6]	462,386	[7]
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	705,578	[5]	581,701	[6]	419,351	[7]
Fair Value, Measurements, Recurring [Member] | U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	59,733		61,295		26,283
Fair Value, Measurements, Recurring [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	146,896		10,989		17,179
Available for sale securities	5,716,525		5,898,351		6,717,569
Fair value option securities	418,887		444,217		434,077
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	58,797		31,901		54,164
Available for sale securities	51,308		56,817		60,818
Fair Value, Measurements, Recurring [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	14,113		18,219		20,418
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,003		995		1,001
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	133,030		139,118		160,031
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,942,404		2,905,796		2,164,842
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	4,151		4,151		9,155
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	19,575		19,672		24,983
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	18,040		17,833		19,776
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	4,219		4,260		6,072
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	29,533		38,530		21,369
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	3,084		0		0
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. 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	1,003		995		1,001
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	3,216		3,265		5,071
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	279,539		122,404		118,044
Available for sale securities	8,868,052		9,024,712		9,138,330
Residential mortgage loans held for sale	323,941		300,565		506,326
Mortgage servicing rights	0		0		0
Derviative contracts, net of cash collateral, Assets, Fair value	760,613		547,740		441,017
Liabilities: [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	702,494		581,701		419,351
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government agency debentures [Member]
Assets: [Abstract]
Trading securities	59,733		61,295		26,283
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. agency residential mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	146,896		10,989		17,179
Available for sale securities	5,716,525		5,898,351		6,717,569
Fair value option securities	418,887		444,217		434,077
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	58,797		31,901		54,164
Available for sale securities	41,694		47,207		51,195
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities [Member]
Assets: [Abstract]
Trading securities	14,113		18,219		20,418
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, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	133,030		139,118		160,031
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	2,942,404		2,905,796		2,164,842
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Available for sale securities	0		0		5,005
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock [Member]
Assets: [Abstract]
Available for sale securities	19,575		19,672		24,983
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds [Member]
Assets: [Abstract]
Available for sale securities	14,824		14,568		14,705
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale securities	13,765		13,761		13,773
Residential mortgage loans held for sale	8,099		7,874		6,870
Mortgage servicing rights	196,055		218,605		175,051
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. 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	9,614		9,610		9,623
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, 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 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 interest rate and agricultural derivative contracts.