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Fair Value Measurements - Additional Information (Detail) $ / shares in Units, $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) Contract $ / shares | Dec. 31, 2016 USD ($) Contract $ / shares | Dec. 31, 2015
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Credit valuation adjustment included in fair value of credit derivative liabilities | $ 60 | $ 1,924 |
Credit valuation adjustment included in fair value of derivative liabilities other than credit derivatives |  | $ 44,973 |
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 | 2.50% | 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 | $ 431,630 | $ 450,307 |
Available-for-sale Securities | $ 5,309,161 | $ 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 | 6.00% | 5.00% |
PercentageofInvestedPortfiliowhereProjectedCashFlowsConsistSolelyofDeferredAmountsandInterest | 13.00% | 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 |
Successor [Member] | Asset-backed Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Coupon rate | 5.97% | 5.93% |
Successor [Member] | Asset-backed Securities [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Available-for-sale Securities | $ 72,540 | $ 65,990 |
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 | 736,017 | 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] | European ABS Transactions [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Fair value of consolidated VIE debt obligations valued using unobservable inputs by asset class | 2,757,688 | 2,551,278 |
Successor [Member] | US Commercial ABS Transaction [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Fair value of consolidated VIE debt obligations valued using unobservable inputs by asset class | $ 0 | $ 30,942 |
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 | 15.00% | 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 | 79.00% | 82.00% |
Underlying, Other [Member] | Successor [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
CVA percentage | 9.64% | 11.14% |
Fair value of derivative liabilities | $ 566 | $ 15,349 |
Notional outstanding | $ 325,890 | $ 737,380 |
Fair Value Input Weighted Average Obligation Price | $ / shares | $ 99.3 | $ 93.5 |
Fair Value Input Weighted Average Life | 6 years 6 months | 5 years 2 months |
Fair Value Input Weighted Average Credit Rating | A | A- |
Fair Value Input Weighted Average Relative Change Ratio | 23.60% | 31.60% |
Variable Interest Entity, Primary Beneficiary [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 | 3.10% | 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 | $ 2,914,145 | $ 2,622,566 |
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | European ABS Transactions [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Coupon rate |  | 0.40% | 0.46%
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | US Commercial ABS Transaction [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Coupon rate | 5.88% |  |
Real Estate [Member] | Successor [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | $ 33,154 | $ 33,303 |
Hedge Funds, Multi-strategy [Member] | Successor [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | 53,054 | 53,985 |
Interest Rate Contract [Member] | Successor [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | 136,603 | 261,315 |
Illiquid Investments [Member] | Successor [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | $ 67,787 | $ 39,068 |
Credit Derivatives [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Number Of Credit Derivative Contracts On Adversely Classified Credit Listing | Contract | 0 | 2 |
Derivative Liability Fair Value For Credit Derivative Contracts On Adversely Classified Credit Listing |  | $ 6,123 |
Notional Principal Outstanding Of Credit Derivative Contracts On Adversely Classified Credit Listing |  | $ 67,783 |

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