Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Detail) (Successor Ambac [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Cash and Securities Pledged Directly from Investment Portfolio [Member]
Investment [Line Items]
Fair Value of Cash and Underlying Securities	$ 497,802	$ 497,946
Fair Value of Cash and Securities Pledged to Investment and Repurchase Agreement Counterparties	372,679	371,723
Fair Value of Cash and Securities Pledged to Derivative Counterparties	125,123	126,223
Cash and Securities Pledged from Its Derivative Counterparties [Member]
Investment [Line Items]
Fair Value of Cash and Underlying Securities		690
Fair Value of Cash and Securities Pledged to Investment and Repurchase Agreement Counterparties
Fair Value of Cash and Securities Pledged to Derivative Counterparties