Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018		Mar. 31, 2018	Dec. 31, 2017
Assets: [Abstract]
Trading securities	$ 2,140,326		$ 1,956,923
Available for sale securities	9,025,198		8,857,120
Fair value option securities	707,994		283,235
Mortgage servicing rights	238,193		259,254		$ 274,978	$ 252,867
Derviative contracts, net of cash collateral, Assets, Fair value	359,223		320,929
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	299,698		362,306
U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	51,576		63,765
Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,952,742		1,791,584
Available for sale securities	6,040,086		5,804,708
Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	50,637		34,507
Available for sale securities	2,447		2,864
Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	40,890		42,656
U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,878		493
Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	47,958		59,736
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,932,357		2,953,889
Other debt securities [Member]
Assets: [Abstract]
Trading securities	44,481		24,411
Available for sale securities	472		35,430
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Trading securities	2,140,326		1,956,923
Available for sale securities	9,025,198		8,857,120
Residential mortgage loans held for sale	160,157		149,221
Mortgage servicing rights	238,193	[1]	259,254	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	359,223	[3]	320,929	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	299,698	[3]	362,306	[4]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	51,576		63,765
Fair Value, Measurements, Recurring [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,952,742		1,791,584
Available for sale securities	6,040,086		5,804,708
Fair value option securities	707,994		283,235
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	50,637		34,507
Available for sale securities	2,447		2,864
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	40,890		42,656
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,878		493
Fair Value, Measurements, Recurring [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	47,958		59,736
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets: [Abstract]
Available for sale securities	2,932,357		2,953,889
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	44,481		24,411
Available for sale securities	472		35,430
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets: [Abstract]
Trading securities	0		0
Available for sale securities	1,878		493
Residential mortgage loans held for sale	0		0
Mortgage servicing rights	0	[1]	0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	4,720	[3]	44,074	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	0	[3]	0	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0		0
Available for sale securities	0		0
Fair value option securities	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
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	1,878		493
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	0		0
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets: [Abstract]
Trading securities	2,140,326		1,956,923
Available for sale securities	9,022,848		8,856,155
Residential mortgage loans held for sale	144,381		134,014
Mortgage servicing rights	0	[1]	0	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	354,503	[3]	276,855	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	299,698	[3]	362,306	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	51,576		63,765
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	1,952,742		1,791,584
Available for sale securities	6,040,086		5,804,708
Fair value option securities	707,994		283,235
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets: [Abstract]
Trading securities	50,637		34,507
Available for sale securities	2,447		2,864
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	40,890		42,656
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury [Member]
Assets: [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	47,958		59,736
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	2,932,357		2,953,889
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	44,481		24,411
Available for sale securities	0		34,958
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets: [Abstract]
Trading securities	0		0
Available for sale securities	472		472
Residential mortgage loans held for sale	15,776		15,207
Mortgage servicing rights	238,193	[1]	259,254	[2]
Derviative contracts, net of cash collateral, Assets, Fair value	0	[3]	0	[4]
Liabilities: [Abstract]
Derivative contracts, net of cash collateral, Liabilities, Fair Value	0	[3]	0	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency debentures [Member]
Assets: [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential agency mortgage-backed securities [Member]
Assets: [Abstract]
Trading securities	0		0
Available for sale securities	0		0
Fair value option securities	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
Available for sale securities			0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed securities [Member]
Assets: [Abstract]
Trading securities	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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential non-agency mortgage-backed securities [Member]
Assets: [Abstract]
Available for sale securities	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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Assets: [Abstract]
Trading securities	0		0
Available for sale securities	$ 472		$ 472

[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] 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 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, fully offset by cash margin.

[4] 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, 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 contracts, fully offset by cash margin.