Investments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified			3 Months Ended	5 Months Ended	4 Months Ended	9 Months Ended									3 Months Ended		4 Months Ended	5 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2012 Predecessor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member]	Sep. 30, 2013 Below Investment Grade Securities and Non-Rated Securities [Member]	Dec. 31, 2012 Below Investment Grade Securities and Non-Rated Securities [Member]	Sep. 30, 2013 Residential Mortgage-Backed Securities [Member]	Sep. 30, 2013 Ambac-wrapped Securities [Member]	Sep. 30, 2013 Other Asset-Backed Securities [Member]	Sep. 30, 2013 Asset Backed, Military Housing, Fixed Rate Securities [Member] Security	Sep. 30, 2013 National Century Financial Enterprises, Inc. [Member]	Mar. 31, 2013 National Century Financial Enterprises, Inc. [Member]	Apr. 30, 2013 National Century Financial Enterprises, Inc. [Member]	Sep. 30, 2013 National Century Financial Enterprises, Inc. [Member]
Investment [Line Items]
Fair value of below investment grade securities and non-rated securities									$ 810,835	$ 192,190
Gross unrealized loss									37,209	43,934
Unrealized losses on securities			101,753	101,753				7,551			21,039	18,369	23,340	22,876
Number of securities in unrealized loss position														6
Investment realized losses				8,162	53,305		70,621									150,201
Investment in asset backed notes																174,500
Cash recoveries						14,007									1,216		39,978	1,216
Securities fair value	6,863	6,945
Fair value of securities held by bankruptcy remote trust	230,049	201,329
Other investments			$ 350	$ (2,665)	$ 369