Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Detail) - Successor [Member] - Cash and Securities Pledged Directly from Investment Portfolio [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Fair Value of Cash and Underlying Securities	$ 348,584	$ 379,423
Fair Value of Cash and Securities Pledged to Investment and Repurchase Agreement Counterparties	108,398	156,916
Fair Value of Cash and Securities Pledged to Derivative Counterparties	$ 240,186	$ 222,507