Comprehensive Income - Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	1 Months Ended	4 Months Ended	6 Months Ended
Jun. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax [Line Items]
Unrealized Gains (Losses) on Available-for-Sale Securities, Net realized investment gains	$ 18,472	$ 7,267	$ 13,349
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	18,472	7,267	13,349
Amortization of Postretirement Benefit, Prior service cost		92	(1,616)
Amortization of Postretirement Benefit, Actuarial gains (losses)		(173)	727
Amortization of Postretirement Benefit, Total before tax		(81)	(889)
Amortization of Postretirement, Tax (expense) benefit		(704)	(704)
Amortization of Postretirement, Net of tax and noncontrolling interest		623	(185)	3,792
Total reclassifications for the period	$ 18,472	$ (7,890)	$ (13,164)

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The total amount reclassified from accumulated other comprehensive income.

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Before tax amount, net of reclassification adjustments, of the (increase) decrease in the value of the projected benefit obligation and the increase (decrease) in the value of the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption that has not been recognized in net periodic benefit cost.

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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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