Comprehensive Income - Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Unrealized Gains (Losses) on Available-for-Sale Securities, Net realized investment gains	$ 6,082
Unrealized Gains (Losses) on Available-for-Sale Securities, Tax (expense) benefit
Unrealized Gains (Losses) on Available-for-Sale Securities, Net of tax and noncontrolling interest	6,082
Amortization of Postretirement Benefit, Prior service cost	(1,707)
Amortization of Postretirement Benefit, Actuarial gains (losses)	899
Amortization of Postretirement Benefit, Total before tax	(808)
Amortization of Postretirement, Tax (expense) benefit
Amortization of Postretirement, Net of tax and noncontrolling interest	(808)	3,792
Total reclassfications for the period	$ 5,274

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The total amount reclassifed from accumulated other comprehensive income.

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The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

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Tax effect of the income statement impact of the reclassification adjustment for prior service costs recognized as a component of net period benefit cost.

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Before tax amount of the income statement impact of the reclassification adjustment for prior service costs recognized as a component of net period benefit cost.

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Net of tax amount of the income statement impact of the reclassification adjustment for prior service costs recognized as a component of net period benefit cost.

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Before tax and reclassification adjustments amount of the change in accumulated other comprehensive income (loss) related to pension and other postretirement benefit plans.

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Before tax amount of the income statement impact of the reclassification adjustment for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Net of tax amount of the income statement impact of the reclassification adjustment for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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