Investments - Summary of Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Successor Ambac [Member]
Investment [Line Items]
Fixed income securities	$ 70,985
Short-term investments	303
Loans	117
Investment expense	(2,598)
Securities available-for-sale and short-term	68,807
Other investments	1,994
Total net investment income	70,801
Predecessor Ambac [Member]
Investment [Line Items]
Fixed income securities		86,331
Short-term investments		595
Loans		108
Investment expense		(1,977)
Securities available-for-sale and short-term		85,057
Other investments		(543)
Total net investment income		84,514
Gains (losses) on securities held as of reporting date [Member] | Successor Ambac [Member]
Investment [Line Items]
Other investments	$ 2,449	$ 614