Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail) (Successor Ambac [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Standard & Poor's, CCC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 2,273,041	$ 1,811,879
Standard & Poor's, A+ Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	269,284
Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	368,818	449,555
Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		570,394
Weighted Average Underlying Rating, BBB- Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	17,444
Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,639	2,917
Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	2,869
Standard & Poor's, B Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,913,782
Standard & Poor's, BB- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		2,855,058
Municipal Bonds [Member] | Standard & Poor's, CCC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	66,213	64,596
Municipal Bonds [Member] | Standard & Poor's, A+ Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	234,577
Municipal Bonds [Member] | Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	290,395	372,392
Municipal Bonds [Member] | Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		532,752
Municipal Bonds [Member] | Weighted Average Underlying Rating, BBB- Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Municipal Bonds [Member] | Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Municipal Bonds [Member] | Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Municipal Bonds [Member] | Standard & Poor's, B Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	591,185
Municipal Bonds [Member] | Standard & Poor's, BB- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		969,740
Corporate Debt Securities [Member] | Standard & Poor's, CCC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Corporate Debt Securities [Member] | Standard & Poor's, A+ Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	34,707
Corporate Debt Securities [Member] | Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	78,423	77,163
Corporate Debt Securities [Member] | Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		37,642
Corporate Debt Securities [Member] | Weighted Average Underlying Rating, BBB- Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		17,444
Corporate Debt Securities [Member] | Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
Corporate Debt Securities [Member] | Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Corporate Debt Securities [Member] | Standard & Poor's, B Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	113,130
Corporate Debt Securities [Member] | Standard & Poor's, BB- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		132,249
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,206,828	1,747,283
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, A+ Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Mortgage and Asset-Backed Securities [Member] | Weighted Average Underlying Rating, BBB- Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
Mortgage and Asset-Backed Securities [Member] | Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,639	2,917
Mortgage and Asset-Backed Securities [Member] | Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	2,869
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, B Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,209,467
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, BB- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		1,753,069
Short-term Investments [Member] | Standard & Poor's, CCC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Standard & Poor's, A+ Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Standard & Poor's, A+ Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Standard & Poor's, AA- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Weighted Average Underlying Rating, BBB- Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Weighted Average Underlying Rating, D Rating [Member] | Assured Guaranty Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Weighted Average Underlying Rating, D Rating [Member] | Financial Guarantee Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors
Short-term Investments [Member] | Standard & Poor's, B Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0
Short-term Investments [Member] | Standard & Poor's, BB- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		$ 0