Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018		Dec. 31, 2017		Mar. 31, 2017		Dec. 31, 2016
Assets: [Abstract]
Trading securities	$ 1,292,432		$ 462,676		$ 677,156
Available for sale debt securities	8,249,432		8,321,578		8,437,291
Fair value option securities	513,668		755,054		441,714
Mortgage servicing rights	274,978		252,867		249,403		$ 247,073
Derviative contracts, net of cash collateral, Assets, Fair value	286,687		220,502		304,727
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	233,202		171,963		276,422
U.S. government agency debentures
Assets: [Abstract]
Trading securities	37,115		21,196		18,365
U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	1,078,085		392,673		578,977
Available for sale debt securities	5,379,921		5,309,152		5,372,916
Fair value option securities	513,668		755,054		441,714
Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	72,013		13,559		45,114
Available for sale debt securities	20,414		27,080		35,453
Other trading securities
Assets: [Abstract]
Trading securities	10,485		11,363		34,700
U.S. Treasury
Assets: [Abstract]
Available for sale debt securities	491		1,000		999
Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale debt securities	90,160		93,221		108,626
Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale debt securities	2,732,966		2,834,961		2,877,028
Other debt securities
Assets: [Abstract]
Available for sale debt securities	25,480		25,481		4,153
Perpetual preferred stock
Assets: [Abstract]
Available for sale debt securities			15,767		19,272
Equity securities and mutual funds
Assets: [Abstract]
Available for sale debt securities			14,916		18,844
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	1,292,432		462,676		677,156
Available for sale debt securities	8,249,432		8,321,578		8,437,291
Residential mortgage loans held for sale	225,190		221,378		248,707
Mortgage servicing rights	274,978	[1]	252,867	[2]	249,403	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	286,687	[4]	220,502	[5]	304,727	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	233,202	[4]	171,963	[5]	276,422	[6]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	37,115		21,196		18,365
Fair Value, Measurements, Recurring [Member] | U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	1,078,085		392,673		578,977
Available for sale debt securities	5,379,921		5,309,152		5,372,916
Fair value option securities	513,668		755,054		441,714
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	72,013		13,559		45,114
Available for sale debt securities	20,414		27,080		35,453
Fair Value, Measurements, Recurring [Member] | Asset-backed securities
Assets: [Abstract]
Trading securities	94,734		23,885
Fair Value, Measurements, Recurring [Member] | Other trading securities
Assets: [Abstract]
Trading securities	10,485		11,363		34,700
Fair Value, Measurements, Recurring [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale debt securities	491		1,000		999
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale debt securities	90,160		93,221		108,626
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale debt securities	2,732,966		2,834,961		2,877,028
Fair Value, Measurements, Recurring [Member] | Other debt securities
Assets: [Abstract]
Available for sale debt securities	25,480		25,481		4,153
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale debt securities			15,767		19,272
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale debt securities			14,916		18,844
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale debt securities	491		1,000		4,905
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	0	[1]	0	[2]	0	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	21,373	[4]	8,179	[5]	12,631	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	16,497	[4]	0	[5]	15,455	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency debentures
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
Assets: [Abstract]
Trading securities	0		0		0
Available for sale debt 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
Assets: [Abstract]
Trading securities	0		0		0
Available for sale debt securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed securities
Assets: [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale debt securities	491		1,000		999
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale debt 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
Assets: [Abstract]
Available for sale debt securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities
Assets: [Abstract]
Available for sale debt securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale debt securities			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale debt securities			0		3,906
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	1,292,432		462,676		677,156
Available for sale debt securities	8,246,578		8,315,304		8,422,511
Residential mortgage loans held for sale	211,319		209,079		236,028
Mortgage servicing rights	0	[1]	0	[2]	0	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	265,314	[4]	212,323	[5]	292,096	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	216,705	[4]	171,963	[5]	260,967	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	37,115		21,196		18,365
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	1,078,085		392,673		578,977
Available for sale debt securities	5,379,921		5,309,152		5,372,916
Fair value option securities	513,668		755,054		441,714
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	72,013		13,559		45,114
Available for sale debt securities	18,523		22,278		29,731
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities
Assets: [Abstract]
Trading securities	94,734		23,885
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	10,485		11,363		34,700
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale debt securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale debt securities	90,160		93,221		108,626
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale debt securities	2,732,966		2,834,961		2,877,028
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities
Assets: [Abstract]
Available for sale debt securities	25,008		25,009		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale debt securities			15,767		19,272
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale debt securities			14,916		14,938
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0		0		0
Available for sale debt securities	2,363		5,274		9,875
Residential mortgage loans held for sale	13,871		12,299		12,679
Mortgage servicing rights	274,978	[1]	252,867	[2]	249,403	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	0	[4]	0	[5]	0	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	0	[4]	0	[5]	0	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency debentures
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
Assets: [Abstract]
Trading securities	0		0		0
Available for sale debt 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
Assets: [Abstract]
Trading securities	0		0		0
Available for sale debt securities	1,891		4,802		5,722
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed securities
Assets: [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale debt securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale debt 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
Assets: [Abstract]
Available for sale debt securities	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities
Assets: [Abstract]
Available for sale debt securities	$ 472		472		4,153
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale debt securities			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale debt securities			$ 0		$ 0

[1] 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 5, Mortgage Banking Activities.

[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 5, 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 5, Mortgage Banking Activities.

[4] 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 interest rate and agricultural derivative contacts. 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.

[5] 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 interest rate, energy and agricultural derivative contacts. 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 energy derivative contracts, fully offset by 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 interest rate and energy derivative contacts. 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 cash margin.