Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended
	Jul. 31, 2015 USD ($)	Mar. 31, 2017 USD ($) Entity	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) Entity
Variable Interest Entities [Line Items]
Equity Method Investments		$ 31,201		$ 30,003
Number of RMBS Sold	17
Cash Received From Delaware Trust	$ 146,000
Secured Debt		92,311		102,403
Fair Value of Securities Placed in Trust		355,223		360,759
Securities Issued by Delaware Trust	$ 146,000
Consolidated VIE assets		13,762,688		13,367,834
Consolidated VIE liabilities		13,631,197		13,235,425
Successor [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity Change in Fair Value of Assets and Liabilities		3,701	$ (27,163)
Fair value of special purpose entities		7,039		7,382
variable interest entities deconsolidation gain loss		0	0
Variable Interest Entity, Measure of Activity, Income or Loss before Tax		$ 3,701	$ (27,163)
Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Weighted average life		4 years 10 months 15 days
Average rating of assets held by sponsored special purpose entities		BBB+
Sponsored Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Total principal amount of debt outstanding		$ 395,490		$ 388,950
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of Newly Consolidated Variable Interest Entities		0	0
Number of DeConsolidated Variable Interest Entities		0	0
Number of consolidated Variable Interest Entities | Entity		12		12
Ambac UK [Member]
Variable Interest Entities [Line Items]
Number of consolidated Variable Interest Entities | Entity		8		8
Consolidated VIE assets		$ 13,362,738		$ 12,950,009
Consolidated VIE liabilities		$ 13,244,407		$ 12,833,466
Ambac Assurance [Member]
Variable Interest Entities [Line Items]
Number of consolidated Variable Interest Entities | Entity		4		4
London Interbank Offered Rate (LIBOR) [Member]
Variable Interest Entities [Line Items]
Interest Rate on Securities Issued by Delaware Trust	2.80%