Income Taxes (Summary Of Effective Income Tax Rate) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Effective Income Tax Rate [Line Items]
Expected income taxes	$ 253,324	$ 262,700	$ 190,250
Tax-exempt investment income	(3,468)	(3,371)	(3,483)
Tax settlements	0	0	(3,101)
Low income housing investments	(24,258)	(12,900)	(6,038)
Other	568	46	1,669
Income tax expense	$ 226,166	$ 246,475	$ 179,297
Expected income taxes, percentage	35.00%	35.00%	35.00%
Tax-exempt investment income, percentage	(0.50%)	(0.50%)	(0.60%)
Tax settlements, percentage	0.00%	0.00%	(0.60%)
Low income housing investments, percentage	(3.40%)	(1.70%)	(1.10%)
Other, percentage	0.10%	0.00%	0.30%
Income tax expense, percentage	31.20%	32.80%	33.00%

Effective Income Tax Rate Reconciliation, Low Income Housing Investments

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This is the reconciling difference between expected and actual tax expense (benefit) for low income housing interests

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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 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 attributable to income that is exempt from income taxes under enacted tax laws.

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The sum of the differences between the effective income tax rate and domestic federal statutory income tax rate attributable to all income tax settlements during the period.

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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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-Glossary Income Tax Expense (or Benefit)

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the year/accounting 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, that is attributable to all other items not otherwise listed in the existing taxonomy.

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The sum of the differences between total income tax expense or benefit as reported in the Income Statement 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 all income tax settlements for the period.

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Interest income derived from securities which are exempt from federal income taxes.

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