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