Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Assets [Abstract]
Trading securities	$ 1,956,923		$ 462,676
Available for sale securities	8,857,120		8,321,578
Fair value option securities	283,235		755,054
Mortgage servicing rights	259,254		252,867		$ 247,073	$ 218,605
Derivative contracts, net of cash margin, Assets, Fair Value	320,929		220,502
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	362,306		171,963
U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	63,765		21,196
U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	1,791,584		392,673
Available for sale securities	5,804,708		5,309,152
Fair value option securities	283,235		755,054
Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	34,507		13,559
Available for sale securities	2,864		27,080
Asset-backed securities [Member]
Assets [Abstract]
Trading securities	42,656		23,885
U.S. Treasury [Member]
Assets [Abstract]
Available for sale securities	493		1,000
Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	59,736		93,221
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	2,953,889		2,834,961
Other debt securities [Member]
Assets [Abstract]
Available for sale securities	35,430		25,481
Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities			15,767
Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities			14,916
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Trading securities	1,956,923		462,676
Available for sale securities	8,857,120		8,321,578
Residential mortgage loans held for sale	149,221		221,378
Mortgage servicing rights	259,254	[1]	252,867	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	320,929	[3]	220,502	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	362,306	[3]	171,963	[4]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	63,765		21,196
Fair Value, Measurements, Recurring [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	1,791,584		392,673
Available for sale securities	5,804,708		5,309,152
Fair value option securities	283,235		755,054
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	34,507		13,559
Available for sale securities	2,864		27,080
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	42,656		23,885
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Assets [Abstract]
Available for sale securities	493		1,000
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	59,736		93,221
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	2,953,889		2,834,961
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets [Abstract]
Trading securities	24,411		11,363
Available for sale securities	35,430		25,481
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities			15,767
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities			14,916
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	493		1,000
Residential mortgage loans held for sale	0		0
Mortgage servicing rights	0	[1]	0	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	44,074	[3]	8,179	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, 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] | U.S. government agency residential 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	493		1,000
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
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 1 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities			0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities			0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Trading securities	1,956,923		462,676
Available for sale securities	8,856,155		8,315,304
Residential mortgage loans held for sale	134,014		209,079
Mortgage servicing rights	0	[1]	0	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	276,855	[3]	212,323	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	362,306	[3]	171,963	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	63,765		21,196
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	1,791,584		392,673
Available for sale securities	5,804,708		5,309,152
Fair value option securities	283,235		755,054
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	34,507		13,559
Available for sale securities	2,864		22,278
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	42,656		23,885
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] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	59,736		93,221
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	2,953,889		2,834,961
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets [Abstract]
Trading securities	24,411		11,363
Available for sale securities	34,958		25,009
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities			15,767
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities			14,916
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	472		5,274
Residential mortgage loans held for sale	15,207		12,299
Mortgage servicing rights	259,254	[1]	252,867	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	0	[3]	0	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, 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] | U.S. government agency residential 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			4,802
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] | Privately issued residential 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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities			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

[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 7, 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 7, Mortgage Banking Activities.

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

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