Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) (USD $)	6 Months Ended				12 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011		Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
US Government Obligations Trading Securities Fair Value Disclosure	$ 53,514,000
US Agency Residential Mortgage Backed Securities Trading Securities Fair Value Disclosure	46,502,000
Municipals And Other Tax Exempt Trading Securities Fair Value Disclosure	44,632,000
Other Trading Securities Fair Value Disclosure	4,669,000
Trading Securities, Fair Value Disclosure	149,317,000
Assets [Abstract]
Trading securities	149,317,000		99,846,000		76,800,000
Available for sale securities [Abstract]
U.S. Treasury	1,003,000		1,003,000		1,006,000
Municipal and other tax-exempt	88,458,000		70,210,000		68,837,000
U.S. agency residential mortgage-backed securities	9,903,532,000		8,893,789,000		9,588,177,000
Private issue residential mortgage-backed securities	317,761,000		513,222,000		419,166,000
Other debt securities	36,286,000		5,893,000		36,495,000
Perpetual preferred stock	23,431,000		22,694,000		18,446,000
Equity securities and mutual funds	24,944,000		60,197,000		47,238,000
US Agency Residential Mortgage Backed Securities Fair Value Option Securities Fair Value Disclosure	299,467,000
Total available for sale securities	10,395,415,000		9,567,008,000		10,179,365,000
Corporate Debt Securities Fair Value Option Securities Fair Value Disclosure	25,710,000
Total fair value option securities	325,177,000
Residential mortgage loans held for sale	259,174,000		169,609,000		188,125,000
Mortgage servicing rights	91,783,000	[1]	109,192,000		86,783,000		98,138,000	120,345,000	115,723,000
Derivative contracts, assets	366,204,000	[2],[3]	229,887,000	[2],[3]	293,859,000	[2],[3]
Other assets - private equity funds	31,492,000		28,313,000		30,902,000
Liabilities [Abstract]
Derivative contracts, liabilities	370,053,000	[2],[3]	173,917,000	[2],[3]	236,522,000	[2],[3]
Investment grade taxable securities par rate of yield (in hundredths)					1.80%
Investment grade taxable securities par rate of yield, lower range (in hundredths)	1.30%		1.69%
Investment grade taxable securities par rate of yield, upper range (in hundredths)	1.75%		1.75%
Average yields on comparable short-term taxable securities, maximum	1.00%		1.00%
Investment grade tax-exempt securities par rate of yield, minimum (in hundredths)	1.00%		1.05%		1.00%
Investment grade tax-exempt securities par rate of yield, maximum (in hundredths)	1.50%		1.35%		1.50%
Investment grade tax-exempt securities yield spread over comparable securities, minimum (in basis points)	75		75
Investment grade tax-exempt securities yield spread over comparable securities, maximum (in basis points)	80		80
Percentage of estimated fair value to par value of tax-exempt securities rated investment grade, minimum (in hundredths)	98.88%		98.89%		98.79%
Percentage of estimated fair value to par value of tax-exempt securities rated investment grade, maximum (in hundredths)	99.49%		99.34%		100.00%
Municipal and tax-exempt securities rated below investment grade	13,000,000		14,000,000		13,000,000
Below investment grade tax-exempt securities par rate of yield, minimum (in hundredths)	6.20%		6.23%		6.25%
Below investment grade tax-exempt securities par rate of yield, maximum (in hundredths)	9.16%		10.30%		9.58%
Below investment grade tax-exempt securities yield spread over comparable securities (in basis points)	600		600
Percentage of estimated fair value to par value of tax exempt securities rated below investment grade minimum (in hundredths)	75.21%		82.66%		76.45%
Percentage of estimated fair value to par value of tax exempt securities rated below investment grade maximum (in hundredths)	75.49%		82.83%		76.99%
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
US Government Obligations Trading Securities Fair Value Disclosure	992,000
US Agency Residential Mortgage Backed Securities Trading Securities Fair Value Disclosure	0
Municipals And Other Tax Exempt Trading Securities Fair Value Disclosure	0
Other Trading Securities Fair Value Disclosure	0
Trading Securities, Fair Value Disclosure	992,000
Assets [Abstract]
Trading securities			2,327,000		0
Available for sale securities [Abstract]
U.S. Treasury	1,003,000		1,003,000		1,006,000
Municipal and other tax-exempt	0		0		0
U.S. agency residential mortgage-backed securities	0		0		0
Private issue residential mortgage-backed securities	0		0		0
Other debt securities	0		0		0
Perpetual preferred stock	0		0		0
Equity securities and mutual funds	6,912,000		41,557,000		23,596,000
US Agency Residential Mortgage Backed Securities Fair Value Option Securities Fair Value Disclosure	0
Total available for sale securities	7,915,000		42,560,000		24,602,000
Corporate Debt Securities Fair Value Option Securities Fair Value Disclosure	0
Total fair value option securities	0
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	0	[1]	0		0
Derivative contracts, assets	802,000	[3]	0	[3]	457,000	[3]
Other assets - private equity funds	0		0		0
Liabilities [Abstract]
Derivative contracts, liabilities	251,000	[3]	0	[3]	0	[3]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
US Government Obligations Trading Securities Fair Value Disclosure	52,522,000
US Agency Residential Mortgage Backed Securities Trading Securities Fair Value Disclosure	46,502,000
Municipals And Other Tax Exempt Trading Securities Fair Value Disclosure	44,632,000
Other Trading Securities Fair Value Disclosure	4,545,000
Trading Securities, Fair Value Disclosure	148,201,000
Assets [Abstract]
Trading securities			97,519,000		76,623,000
Available for sale securities [Abstract]
U.S. Treasury	0		0		0
Municipal and other tax-exempt	46,796,000		26,552,000		26,484,000
U.S. agency residential mortgage-backed securities	9,903,532,000		8,893,789,000		9,588,177,000
Private issue residential mortgage-backed securities	317,761,000		513,222,000		419,166,000
Other debt securities	30,898,000		0		30,595,000
Perpetual preferred stock	23,431,000		22,694,000		18,446,000
Equity securities and mutual funds	18,032,000		18,640,000		23,642,000
US Agency Residential Mortgage Backed Securities Fair Value Option Securities Fair Value Disclosure	299,467,000
Total available for sale securities	10,340,450,000		9,474,897,000		10,106,510,000
Corporate Debt Securities Fair Value Option Securities Fair Value Disclosure	25,710,000
Total fair value option securities	325,177,000
Residential mortgage loans held for sale	259,174,000		169,609,000		188,125,000
Mortgage servicing rights	0	[1]	0		0
Derivative contracts, assets	365,402,000	[3]	229,887,000	[3]	293,402,000	[3]
Other assets - private equity funds	0				0
Liabilities [Abstract]
Derivative contracts, liabilities	369,802,000	[3]	173,917,000	[3]	236,522,000	[3]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
US Government Obligations Trading Securities Fair Value Disclosure	0
US Agency Residential Mortgage Backed Securities Trading Securities Fair Value Disclosure	0
Municipals And Other Tax Exempt Trading Securities Fair Value Disclosure	1,852,000
Other Trading Securities Fair Value Disclosure	124,000
Trading Securities, Fair Value Disclosure	1,976,000
Assets [Abstract]
Trading securities			0		177,000
Available for sale securities [Abstract]
U.S. Treasury	0		0		0
Municipal and other tax-exempt	41,662,000		43,658,000		42,353,000
U.S. agency residential mortgage-backed securities	0		0		0
Private issue residential mortgage-backed securities	0		0		0
Other debt securities	5,388,000		5,893,000		5,900,000
Perpetual preferred stock	0		0		0
Equity securities and mutual funds	0		0		0
US Agency Residential Mortgage Backed Securities Fair Value Option Securities Fair Value Disclosure	0
Total available for sale securities	47,050,000		49,551,000		48,253,000
Corporate Debt Securities Fair Value Option Securities Fair Value Disclosure	0
Total fair value option securities	0
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	91,783,000	[1]	109,192,000	[1]	86,783,000	[1]
Derivative contracts, assets	0	[3]	0	[3]	0	[3]
Other assets - private equity funds	31,492,000		28,313,000		30,902,000
Liabilities [Abstract]
Derivative contracts, liabilities	$ 0	[3]	$ 0	[3]	$ 0	[3]

[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] Derivative contracts are recorded on a net basis in the balance sheet in recognition of master netting agreements that enable the Company to settle all derivative positions with a given counterparty in total and to offset the net derivative position with the related cash collateral.

[3] See Note 3 for detail of fair value of derivative contracts by contract type.