Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments	$ 391,075	$ 285,261
Notional outstanding	820,988	970,883
Other Contracts [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding		$ 58,482
Weighted average life (WAL) in years		2 months
Weighted average credit rating		A+
CVA percentage		0.09%
Fair value of derivative liabilities		$ 9
Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	820,988	970,883
Successor [Member] | CLO [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	$ 176,384	$ 295,253
Weighted average reference obligation price	$ 99.3	$ 98.4
Weighted average life (WAL) in years	8 months	1 year 1 month
Weighted average credit rating	AA	AA
Weighted average relative change ratio	36.60%	36.30%
CVA percentage	5.93%	8.34%
Fair value of derivative liabilities	$ 399	$ 1,837
Successor [Member] | Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	$ 644,604	$ 617,148
Weighted average reference obligation price	$ 92.2	$ 85.2
Weighted average life (WAL) in years	6 years 2 months	6 years 1 month
Weighted average credit rating	BBB+	BBB+
Weighted average relative change ratio	31.00%	33.30%
CVA percentage	14.37%	23.34%
Fair value of derivative liabilities	$ 16,301	$ 32,697
Real Estate [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments	34,412	59,719
Hedge Funds, Multi-strategy [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments	55,884	35,464
Interest Rate Contract [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments	182,391	99,579
Illiquid Investments [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments	$ 39,816	$ 44,754
Asset-backed Securities [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs Coupon Rate	5.96%
Fair Value Inputs Maturity	17 years 11 months 5 days
Fair Value Inputs Yield	12.00%
Variable Interest Entity, Primary Beneficiary [Member] | US Commercial ABS Transaction [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs Coupon Rate	5.88%	5.88%
Fair Value Inputs Maturity	21 years 1 month 5 days	21 years 9 months 23 days
Fair Value Inputs Yield	5.90%	9.14%
Variable Interest Entity, Primary Beneficiary [Member] | European Transactions [Member] | Successor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs Coupon Rate	0.47%	1.38%
Fair Value Inputs Maturity	16 years 4 months 28 days	16 years 5 months 9 days
Fair Value Inputs Yield	5.25%	6.08%