Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified			4 Months Ended	3 Months Ended	5 Months Ended	9 Months Ended	4 Months Ended	3 Months Ended	5 Months Ended	9 Months Ended	4 Months Ended	3 Months Ended	5 Months Ended	9 Months Ended	4 Months Ended	3 Months Ended	5 Months Ended	9 Months Ended
Sep. 30, 2014	Dec. 31, 2013	Apr. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2014 Successor [Member]	Sep. 30, 2013 Successor [Member]	Sep. 30, 2013 Successor [Member]	Sep. 30, 2014 Successor [Member]	Apr. 30, 2013 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Predecessor Ambac [Member]	Sep. 30, 2014 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Successor [Member]	Sep. 30, 2013 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Successor [Member]	Sep. 30, 2013 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Successor [Member]	Sep. 30, 2014 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Successor [Member]	Apr. 30, 2013 Other Postretirement Benefit Plan, Defined Benefit [Member] Predecessor Ambac [Member]	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member] Successor [Member]	Sep. 30, 2013 Other Postretirement Benefit Plan, Defined Benefit [Member] Successor [Member]	Sep. 30, 2013 Other Postretirement Benefit Plan, Defined Benefit [Member] Successor [Member]	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member] Successor [Member]	Apr. 30, 2013 Accumulated Translation Adjustment [Member] Predecessor Ambac [Member]	Sep. 30, 2014 Accumulated Translation Adjustment [Member] Successor [Member]	Sep. 30, 2013 Accumulated Translation Adjustment [Member] Successor [Member]	Sep. 30, 2013 Accumulated Translation Adjustment [Member] Successor [Member]	Sep. 30, 2014 Accumulated Translation Adjustment [Member] Successor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 250,865	$ 11,661	$ 625,385	$ 306,328	$ (103,507)	$ 0	$ 11,661	$ 651,272	$ 231,975	$ (90,983)	$ 0	$ (41,910)	$ (5,860)	$ 10,439	$ 0	$ 0	$ 10,847	$ (20,027)	$ 63,914	$ (12,524)	$ 0	$ 42,724
Other comprehensive income before reclassifications			188,039	(50,256)	43,700	(43,335)	245,035	188,696	(12,222)	4,316	(70,195)	261,879	0	0	0	0	0	(657)	(38,034)	39,384	26,860	(16,844)
Amounts reclassified from accumulated other comprehensive income			(13,164)	(5,207)	49,561	33,089	(5,831)	(13,349)	(5,003)	49,561	33,089	(5,219)	185	(204)	0	0	(612)				0	0
Elimination Of Predecessor Shareholder Equity And Noncontrolling Interest			(800,260)					(826,619)					5,675					20,684
Net current period other comprehensive income			(625,385)	(55,463)	93,261	(10,246)	239,204	(651,272)	(17,225)	53,877	(37,106)	256,660	5,860	(204)	0	0	(612)	20,027	(38,034)	39,384	26,860	(16,844)
Ending Balance	$ 250,865	$ 11,661	$ 0	$ 250,865	$ (10,246)	$ (10,246)	$ 250,865	$ 0	$ 214,750	$ (37,106)	$ (37,106)	$ 214,750	$ 0	$ 10,235	$ 0	$ 0	$ 10,235	$ 0	$ 25,880	$ 26,860	$ 26,860	$ 25,880

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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