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Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2016 | Mar. 31, 2017 | Dec. 31, 2016
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Credit valuation adjustment included in fair value of credit derivative liabilities |  | $ 1,810 | $ 1,924
Credit valuation adjustment included in fair value of derivative liabilities other than credit derivatives |  | 42,894 | $ 44,943
Additional basis point fee need to receive for issuing a CDS on obligation | 0.05% |  |
Additional basis points fee increase on change of reference obligation spread | 0.15% |  |
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs |  |  | 2.60%
Minimum [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Basis point fee received for issuing a CDS on reference obligation base fee | 0.20% |  |
Credit spread of reference obligation of a base transaction | 0.80% |  |
Maximum [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Basis point fee received for issuing a CDS on reference obligation hypothetical fee | 0.25% |  |
Credit spread of reference obligation of revised transaction | 1.00% |  |
Successor [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other investments |  | 478,688 | $ 450,307
Notional outstanding |  | $ 722,492 | 737,380
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs |  | 2.60% |
Available-for-sale Securities |  | $ 5,855,962 | $ 6,049,908
Successor [Member] | Fixed Income Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Percentage of investment portfolio valued using dealer quotes |  | 5.00% | 5.00%
PercentageofInvestedPortfiliowhereProjectedCashFlowsConsistSolelyofDeferredAmountsandInterest |  | 11.00% | 12.00%
Successor [Member] | U.S. Agency Obligations [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Available-for-sale Securities |  | $ 0 | $ 0
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Available-for-sale Securities |  | 655,817 | 696,713
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Available-for-sale Securities |  | 0 | 0
Successor [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Available-for-sale Securities |  | $ 0 | $ 0
Successor [Member] | Minimum [Member] | Fixed Income Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Percentage of investment portfolio valued using internal valuation models |  | 12.00% | 13.00%
Successor [Member] | Maximum [Member] | Fixed Income Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Percentage of investment portfolio valued using external pricing services |  | 83.00% | 82.00%
Variable Interest Entities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs |  | 3.30% | 3.60%
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | Corporate Obligations [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Available-for-sale Securities |  | $ 2,663,719 | $ 2,622,566

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