Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail) - Successor [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Standard & Poor's, AA Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 6,000	$ 5,998
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	18,913	20,733
Standard & Poor's, CC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		3,468,993
Standard & Poor's, CC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,883,013	3,442,262
Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,907,926
Municipal Bonds [Member] | Standard & Poor's, AA Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	6,000	5,998
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	18,913	20,733
Municipal Bonds [Member] | Standard & Poor's, CC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		733,446
Municipal Bonds [Member] | Standard & Poor's, CC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	785,791	706,715
Municipal Bonds [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	810,704
Corporate Debt Securities [Member] | Standard & Poor's, AA Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
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	0	0
Corporate Debt Securities [Member] | Standard & Poor's, CC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		32,660
Corporate Debt Securities [Member] | Standard & Poor's, CC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	813,720	32,660
Corporate Debt Securities [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	813,720
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		2,702,887
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CC Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	1,283,502	$ 2,702,887
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 1,283,502