Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) (USD $)	9 Months Ended				12 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Dec. 31, 2010		Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2009
Assets [Abstract]
Trading securities	$ 109,659,000		$ 82,247,000		$ 55,467,000
Available for sale securities [Abstract]
Mortgage trading securities	672,191,000		475,215,000		428,021,000
Residential mortgage loans held for sale	256,397,000		316,893,000		263,413,000
Mortgage servicing rights	87,948,000		86,333,000		115,723,000		109,192,000	98,942,000	73,824,000
Derivative contracts, assets	370,616,000		266,104,000		270,445,000
Liabilities [Abstract]
Certificates of deposit			28,000,000
Derivative contracts, liabilities	341,822,000		218,296,000		215,420,000
Investment grade taxable securities par rate of yield (in hundredths)					1.76%
Investment grade taxable securities par rate of yield, lower range (in hundredths)	1.64%		1.74%
Investment grade taxable securities par rate of yield, upper range (in hundredths)	1.73%		3.29%		1.76%
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%		1.04%		1.15%
Investment grade tax-exempt securities par rate of yield, maximum (in hundredths)	1.30%		1.10%		1.45%
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)	98.99%		99.05%		99.08%
Percentage of estimated fair value to par value of tax-exempt securities rated investment grade, maximum (in hundredths)	100.00%		99.67%		100.00%
Municipal and tax-exempt securities rated below investment grade	14,000,000		11,500,000		11,000,000
Below investment grade tax-exempt securities par rate of yield, minimum (in hundredths)	6.25%		4.55%		4.62%
Below investment grade tax-exempt securities par rate of yield, maximum (in hundredths)	9.55%		7.93%		8.93%
Below investment grade tax-exempt securities yield spread over comparable securities (in basis points)	600		425		425
Percentage of estimated fair value to par value of tax exempt securities rated below investment grade minimum (in hundredths)	83.35%		85.60%		85.13%
Percentage of estimated fair value to par value of tax exempt securities rated below investment grade maximum (in hundredths)	83.57%		86.17%		85.34%
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Available for sale securities [Abstract]
Impaired loans	0		0
Real Estate And Other Repossessed Assets	0		0
Other assets - alternative investments			0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available for sale securities [Abstract]
Impaired loans	13,605,000		40,665,000
Real Estate And Other Repossessed Assets	24,968,000		29,480,000
Other assets - alternative investments			0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available for sale securities [Abstract]
Impaired loans	2,086,000		635,000
Real Estate And Other Repossessed Assets	0		5,631,000
Other assets - alternative investments			2,950,000
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Trading securities	109,659,000		82,247,000		55,467,000
Available for sale securities [Abstract]
U.S. Treasury	1,006,000
Municipal and other tax-exempt	70,195,000		68,308,000		72,942,000
U.S. agency residential mortgage-backed securities	9,016,877,000		8,596,911,000		8,446,908,000
Private issue residential mortgage-backed securities	457,332,000		708,472,000		644,210,000
Other debt securities	5,900,000		9,887,000		6,401,000
Perpetual preferred stock	19,080,000		22,024,000		22,114,000
Equity securities and mutual funds	49,241,000		44,669,000		43,046,000
Total available for sale securities	9,619,631,000		9,450,271,000		9,235,621,000
Mortgage trading securities	672,191,000		475,215,000		428,021,000
Residential mortgage loans held for sale	256,397,000		316,893,000		263,413,000
Mortgage servicing rights	87,948,000	[1]	86,333,000		115,723,000
Derivative contracts, assets	370,616,000	[2]	266,104,000	[2]	270,445,000	[2]
Other assets - private equity funds	29,113,000		23,831,000		25,436,000
Liabilities [Abstract]
Certificates of deposit			27,804,000		27,414,000
Derivative contracts, liabilities	341,822,000		218,296,000	[2]	215,420,000	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Trading securities	888,000		4,219,000		877,000
Available for sale securities [Abstract]
U.S. Treasury	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	29,827,000		21,426,000		22,344,000
Total available for sale securities	30,833,000		21,426,000		22,344,000
Mortgage trading securities	0		0		0
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	0	[1]	0		0
Derivative contracts, assets	34,770,000	[2]	0	[2]	0	[2]
Other assets - private equity funds	0		0		0
Liabilities [Abstract]
Certificates of deposit			0		0
Derivative contracts, liabilities	0		0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Trading securities	108,771,000		78,028,000		54,590,000
Available for sale securities [Abstract]
U.S. Treasury	0
Municipal and other tax-exempt	26,483,000		27,397,000		25,849,000
U.S. agency residential mortgage-backed securities	9,016,877,000		8,596,911,000		8,446,908,000
Private issue residential mortgage-backed securities	457,332,000		708,472,000		644,210,000
Other debt securities	0		3,000		1,000
Perpetual preferred stock	19,080,000		22,024,000		22,114,000
Equity securities and mutual funds	19,414,000		23,243,000		20,702,000
Total available for sale securities	9,539,186,000		9,378,050,000		9,159,784,000
Mortgage trading securities	672,191,000		475,215,000		428,021,000
Residential mortgage loans held for sale	256,397,000		316,893,000		263,413,000
Mortgage servicing rights	0	[1]	0		0
Derivative contracts, assets	335,846,000	[2]	266,104,000	[2]	270,445,000	[2]
Other assets - private equity funds	0		0		0
Liabilities [Abstract]
Certificates of deposit			27,804,000		27,414,000
Derivative contracts, liabilities	341,822,000		218,296,000	[2]	215,420,000	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Trading securities	0		0		0
Available for sale securities [Abstract]
U.S. Treasury	0
Municipal and other tax-exempt	43,712,000		40,911,000		47,093,000
U.S. agency residential mortgage-backed securities	0		0		0
Private issue residential mortgage-backed securities	0		0		0
Other debt securities	5,900,000		9,884,000		6,400,000
Perpetual preferred stock	0		0		0
Equity securities and mutual funds	0		0		0
Total available for sale securities	49,612,000		50,795,000		53,493,000
Mortgage trading securities	0		0		0
Residential mortgage loans held for sale	0		0		0
Mortgage servicing rights	87,948,000	[1]	86,333,000	[1]	115,723,000	[1]
Derivative contracts, assets	0	[2]	0	[2]	0	[2]
Other assets - private equity funds	29,113,000		23,831,000		25,436,000
Liabilities [Abstract]
Certificates of deposit			0		0
Derivative contracts, liabilities	0		0	[2]	0	[2]
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Available for sale securities [Abstract]
U.S. Treasury	1,006,000
Municipal and other tax-exempt	70,195,000		68,308,000		72,942,000
U.S. agency residential mortgage-backed securities	9,016,877,000		8,596,911,000		8,446,908,000
Private issue residential mortgage-backed securities	457,332,000		708,472,000		644,210,000
Other debt securities	5,900,000		9,887,000		6,401,000
Perpetual preferred stock	19,080,000		22,024,000		22,114,000
Equity securities and mutual funds	49,241,000		44,669,000		43,046,000
Total available for sale securities	9,619,631,000		9,450,271,000		9,235,621,000
Mortgage trading securities	672,191,000		475,215,000		428,021,000
Residential mortgage loans held for sale	256,397,000		316,893,000		263,413,000
Mortgage servicing rights	87,948,000		86,333,000		115,723,000
Derivative contracts, assets	370,616,000		266,104,000		270,445,000
Other assets - alternative investments	29,113,000		23,831,000		25,436,000
Liabilities [Abstract]
Derivative contracts, liabilities	341,822,000		218,296,000		215,420,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Available for sale securities [Abstract]
U.S. Treasury	1,006,000
Municipal and other tax-exempt	70,195,000		68,308,000		72,942,000
U.S. agency residential mortgage-backed securities	9,016,877,000		8,596,911,000		8,446,908,000
Private issue residential mortgage-backed securities	457,332,000		708,472,000		644,210,000
Other debt securities	5,900,000		9,887,000		6,401,000
Perpetual preferred stock	19,080,000		22,024,000		22,114,000
Equity securities and mutual funds	49,241,000		44,669,000		43,046,000
Total available for sale securities	9,619,631,000		9,450,271,000		9,235,621,000
Mortgage trading securities	672,191,000		475,215,000		428,021,000
Residential mortgage loans held for sale	256,397,000		316,893,000		263,413,000
Mortgage servicing rights	87,948,000		86,333,000		115,723,000
Derivative contracts, assets	370,616,000		266,104,000		270,445,000
Other assets - alternative investments	29,113,000		23,831,000		25,436,000
Liabilities [Abstract]
Derivative contracts, liabilities	$ 341,822,000		$ 218,296,000		$ 215,420,000

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