Federal and State Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Amount [Abstract]
Federal statutory tax	$ 42,459	$ 53,414	$ 90,113	$ 98,463
Tax exempt revenue	(1,803)	(1,334)	(3,545)	(2,598)
Effect of state income taxes, net of federal benefit	3,122	3,572	6,500	6,570
Utilization of tax credits	(1,826)	(1,467)	(3,548)	(2,564)
Bank-owned life insurance	(993)	(976)	(1,878)	(1,955)
Other, net	464	(60)	877	753
Total	$ 41,423	$ 53,149	$ 88,519	$ 98,669
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%	2.00%
Utilization of tax credits (in hundredths)	(2.00%)	(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%	0.00%	1.00%
Total (in hundredths)	34.00%	35.00%	34.00%	35.00%

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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 attributable to all other items 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 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 portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to other deductions received under enacted tax laws not otherwise listed in the existing taxonomy.

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