Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) (Successor Ambac [Member])	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Corporate Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	0.35%	0.35%
Maturity	19 years 4 months 21 days	20 years 1 month 19 days
Yield	5.23%	6.30%
U.S. Agency Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate		6.98%
Maturity		1 year 4 months 13 days
Yield		0.39%
Asset-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	0.63%	0.64%
Maturity	6 years 8 months 9 days	7 years 1 month 25 days
Yield	4.72%	5.17%