Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018		Mar. 31, 2018	Dec. 31, 2017		Jun. 30, 2017		Mar. 31, 2017	Dec. 31, 2016
Assets: [Abstract]
Trading securities	$ 1,909,615			$ 462,676		$ 441,414
Available for sale securities	8,162,866			8,321,578		8,341,041
Fair value option securities	482,227			755,054		445,169
Mortgage servicing rights	278,719		$ 274,978	252,867		245,239		$ 249,403	$ 247,073
Derviative contracts, net of cash collateral, Assets, Fair value	373,373			220,502		280,289
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	234,856			171,963		285,819
U.S. government agency debentures
Assets: [Abstract]
Trading securities	28,750			21,196		20,954
U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	1,605,001			392,673		365,171
Available for sale securities	5,304,560			5,309,152		5,382,377
Fair value option securities	482,227			755,054		445,169
Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	70,606			13,559		45,444
Available for sale securities	10,697			27,080		32,765
Other trading securities
Assets: [Abstract]
Trading securities	11,987			11,363		9,845
U.S. Treasury
Assets: [Abstract]
Available for sale securities	490			1,000		998
Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale securities	83,224			93,221		103,383
Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale securities	2,738,451			2,834,961		2,782,070
Other debt securities
Assets: [Abstract]
Available for sale securities	25,444			25,481		4,152
Perpetual preferred stock
Assets: [Abstract]
Available for sale securities				15,767		16,568
Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities				14,916		18,728
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	1,909,615			462,676		441,414
Available for sale securities	8,162,866			8,321,578		8,341,041
Residential mortgage loans held for sale	223,301			221,378		287,259
Mortgage servicing rights	278,719	[1]		252,867	[2]	245,239	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	373,373	[4]		220,502	[5]	280,289	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	234,856	[4]		171,963	[5]	285,819	[6]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	28,750			21,196		20,954
Fair Value, Measurements, Recurring [Member] | U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	1,605,001			392,673		365,171
Available for sale securities	5,304,560			5,309,152		5,382,377
Fair value option securities	482,227			755,054		445,169
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	70,606			13,559		45,444
Available for sale securities	10,697			27,080		32,765
Fair Value, Measurements, Recurring [Member] | Asset-backed securities
Assets: [Abstract]
Trading securities	193,271			23,885
Fair Value, Measurements, Recurring [Member] | Other trading securities
Assets: [Abstract]
Trading securities	11,987			11,363		9,845
Fair Value, Measurements, Recurring [Member] | U.S. Treasury
Assets: [Abstract]
Available for sale securities	490			1,000		998
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities
Assets: [Abstract]
Available for sale securities	83,224			93,221		103,383
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies
Assets: [Abstract]
Available for sale securities	2,738,451			2,834,961		2,782,070
Fair Value, Measurements, Recurring [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	25,444			25,481		4,152
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale securities				15,767		16,568
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities				14,916		18,728
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	490			1,000		4,514
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	21,056	[4]		8,179	[5]	46,366	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	17,214	[4]		0	[5]	20,915	[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 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 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 securities	490			1,000		998
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities
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
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale securities				0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities				0		3,516
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	1,909,615			462,676		441,414
Available for sale securities	8,159,875			8,315,304		8,327,720
Residential mortgage loans held for sale	209,058			209,079		274,524
Mortgage servicing rights	0	[1]		0	[2]	0	[3]
Derviative contracts, net of cash collateral, Assets, Fair value	352,317	[4]		212,323	[5]	233,923	[6]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	217,642	[4]		171,963	[5]	264,904	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures
Assets: [Abstract]
Trading securities	28,750			21,196		20,954
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency residential mortgage-backed securities
Assets: [Abstract]
Trading securities	1,605,001			392,673		365,171
Available for sale securities	5,304,560			5,309,152		5,382,377
Fair value option securities	482,227			755,054		445,169
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities
Assets: [Abstract]
Trading securities	70,606			13,559		45,444
Available for sale securities	8,667			22,278		28,110
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities
Assets: [Abstract]
Trading securities	193,271			23,885
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities
Assets: [Abstract]
Trading securities	11,987			11,363		9,845
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury
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
Assets: [Abstract]
Available for sale securities	83,224			93,221		103,383
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 securities	2,738,451			2,834,961		2,782,070
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	24,973			25,009		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale securities				15,767		16,568
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale securities				14,916		15,212
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0			0		0
Available for sale securities	2,501			5,274		8,807
Residential mortgage loans held for sale	14,243			12,299		12,735
Mortgage servicing rights	278,719	[1]		252,867	[2]	245,239	[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 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 securities	2,030			4,802		4,655
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 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 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 securities	0			0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities
Assets: [Abstract]
Available for sale securities	$ 471			472		4,152
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock
Assets: [Abstract]
Available for sale securities				0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and mutual funds
Assets: [Abstract]
Available for sale 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 6, 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 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] 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, net of cah margin. Derivative contacts in liability positions that were valued using quoted prices in active markets for identical instruments are exchange-traded energy and interest rate 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 energy and interest rate 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.