Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 Residential Mortgage-Backed Securities [Member]	Jun. 30, 2013 Other asset-backed securities [Member]	Dec. 31, 2012 Predecessor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Short-Term [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member] Municipal Obligations [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member] Corporate Obligations [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member] U.S. government obligations [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member] Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member] Collateralized Debt Obligations [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Fixed income securities [Member] Other asset-backed securities [Member]	Jun. 30, 2013 Successor Ambac [Member]	Jun. 30, 2013 Successor Ambac [Member] Short-Term [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] Municipal Obligations [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] Corporate Obligations [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] U.S. government obligations [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] Residential Mortgage-Backed Securities [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] Collateralized Debt Obligations [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] Other asset-backed securities [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] Foreign obligations [Member]	Jun. 30, 2013 Successor Ambac [Member] Fixed income securities [Member] U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value			$ 228,442	$ 1,194	$ 227,248	$ 42,503	$ 69,727	$ 26,081	$ 88,504	$ 253	$ 180	$ 4,152,522	$ 658	$ 4,151,864	$ 1,596,765	$ 926,601	$ 282,309	$ 640,736	$ 18,823	$ 549,562	$ 88,111	$ 48,957
Less than 12 Months, Gross Unrealized Loss	23,426	23,570	7,551		7,551	354	1,081	626	5,319	168	3	137,749	4	137,745	59,103	26,437	791	23,426	178	23,570	4,092	148
12 Months or More, Fair Value					455,626	4,303	132,916		116,146	13,429	188,832
12 Months or More, Fair Value			455,626
12 Months or More, Gross Unrealized Loss					70,164	29	8,036		15,236	360	46,503
12 Months or More, Gross Unrealized Losses			70,164
Total, Fair Value					682,874	46,806	202,643	26,081	204,650	13,682	189,012
Total, Fair Value			684,068	1,194
Total, Gross Unrealized Loss					77,715	383	9,117	626	20,555	528	46,506
Total, Gross Unrealized Loss			$ 77,715									$ 137,749