Net Income Per Share - Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share (Detail)	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	4 Months Ended
	Sep. 30, 2014 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2014 Successor Ambac [Member]	Sep. 30, 2014 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2013 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2013 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2014 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2014 Successor Ambac [Member] Restricted Stock Units [Member]	Sep. 30, 2013 Successor Ambac [Member] Restricted Stock Units [Member]	Sep. 30, 2013 Successor Ambac [Member] Restricted Stock Units [Member]	Sep. 30, 2014 Successor Ambac [Member] Restricted Stock Units [Member]	Sep. 30, 2014 Successor Ambac [Member] Performance Shares [Member]	Sep. 30, 2013 Successor Ambac [Member] Performance Shares [Member]	Sep. 30, 2013 Successor Ambac [Member] Performance Shares [Member]	Sep. 30, 2014 Successor Ambac [Member] Performance Shares [Member]	Sep. 30, 2014 Successor Ambac [Member] Warrants [Member]	Sep. 30, 2013 Successor Ambac [Member] Warrants [Member]	Sep. 30, 2013 Successor Ambac [Member] Warrants [Member]	Sep. 30, 2014 Successor Ambac [Member] Warrants [Member]	Sep. 30, 2014 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2013 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2013 Successor Ambac [Member] Employee Stock Option [Member]	Sep. 30, 2014 Successor Ambac [Member] Employee Stock Option [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Employee Stock Option [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Restricted Stock Units [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Performance Shares [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Warrants [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of common shares used for basic earnings per share	45,115,882	45,002,463	45,001,741	45,083,831																					302,469,544
Effect of potential dilutive shares:
Effect of potential dilutive shares									31,384	0	0	40,473	0	0	0	0	1,469,203	1,352,412	1,443,874	1,892,211	8,220	0	0	10,569			109,701	0	0	0
Weighted average number of common shares and potential dilutive shares used for diluted earnings per share	46,624,689	46,354,875	46,445,615	47,027,084																					302,579,245
Anti-dilutive shares excluded from reconciliation																										475,550