Investments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended		4 Months Ended					3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended	0 Months Ended	4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2014 Successor Ambac [Member]	Dec. 31, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2014 Below Investment Grade Securities and Non-Rated Securities [Member] Successor Ambac [Member]	Dec. 31, 2013 Below Investment Grade Securities and Non-Rated Securities [Member] Successor Ambac [Member]	Sep. 30, 2014 Residential Mortgage-Backed Securities [Member] Successor Ambac [Member]	Sep. 30, 2014 Ambac Wrapped Securities [Member] Successor Ambac [Member]	Sep. 30, 2014 Gains (losses) on securities held as of reporting date [Member] Successor Ambac [Member]	Sep. 30, 2013 Gains (losses) on securities held as of reporting date [Member] Successor Ambac [Member]	Apr. 30, 2013 Gains (losses) on securities held as of reporting date [Member] Successor Ambac [Member]	Sep. 30, 2013 Gains (losses) on securities held as of reporting date [Member] Successor Ambac [Member]	Sep. 30, 2014 Gains (losses) on securities held as of reporting date [Member] Successor Ambac [Member]	Dec. 06, 2013 National Century Financial Enterprises, Inc. [Member]	Apr. 30, 2013 National Century Financial Enterprises, Inc. [Member]	Jun. 30, 2013 National Century Financial Enterprises, Inc. [Member]	Sep. 30, 2014 National Century Financial Enterprises, Inc. [Member]
Investment [Line Items]
Fair value of below investment grade securities and non-rated securities									$ 240,497	$ 826,969
Gross unrealized loss									11,202	36,946
Payment of permitted policy claim (percent)	25.00%
Future payment of permitted policy claim (percent)	45.00%
Unrealized losses on securities			15,198			15,198	116,634
Investment realized losses					8,162	29,401		53,305
Cash recoveries	7,760																	1,441	39,978	39,978	0
Securities fair value	6,766	6,799
Fair value of securities held by bankruptcy remote trust	0	240,150
Other investments			700	350	(2,665)	5,905		369					329	1,577	(78)	(784)	5,965
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments			$ 31,485			$ 31,485	$ 116,634				$ 8,608	$ 6,805