Federal and State Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Amount [Abstract]
Federal statutory tax	$ 53,414	$ 38,868	$ 98,463	$ 75,100
Tax exempt revenue	(1,334)	(1,331)	(2,598)	(2,694)
Effect of state income taxes, net of federal benefit	3,572	2,738	6,570	5,376
Utilization of tax credits	(1,467)	(594)	(2,564)	(1,093)
Bank-owned life insurance	(976)	(979)	(1,955)	(1,964)
Other, net	(60)	655	753	3,384
Total	$ 53,149	$ 39,357	$ 98,669	$ 78,109
Percent of pretax income [Abstract]
Federal statutory tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Tax exempt revenue (in hundredths)	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Effect of state income taxes, net of federal benefit (in hundredths)	3.00%	3.00%	2.00%	3.00%
Utilization of tax credits (in hundredths)	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Bank-owned life insurance (in hundredths)	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Other, net (in hundredths)	0.00%	0.00%	1.00%	1.00%
Total (in hundredths)	35.00%	35.00%	35.00%	36.00%

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to other deductions received under enacted tax laws not otherwise listed in the existing taxonomy.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the state and local income tax expense or benefit, net of the federal tax benefit (expense) thereon, recorded during the period.

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The sum of the differences between the effective income tax rate and domestic federal statutory income tax rate that can be explained by all tax credits generated or utilized under enacted tax laws during the period.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to income that is exempt from income taxes under enacted tax laws.

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The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

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