Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	$ 5,855,962	$ 6,049,908
Ambac insured Re-remic [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	1.48%
Fair Value Inputs Maturity	4 years 3 months 26 days
Yield	0.00%
Variable Interest Entity, Primary Beneficiary [Member] | United States Transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	5.88%	5.88%
Fair Value Inputs Maturity	20 years 7 months 5 days	20 years 8 months 68 days
Yield	5.95%	5.86%
Fair Value, Inputs, Level 3 [Member] | RMBS Cash Flows Consisting of Deferred Amounts [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	$ 628,986	$ 696,713
Fair Value, Inputs, Level 3 [Member] | RMBS priced using discounted cash flows [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	26,831
Fair Value, Inputs, Level 3 [Member] | Ambac insured Re-remic [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		0
Fair Value, Inputs, Level 3 [Member] | Corporate Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	0	0
Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Corporate Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	$ 2,663,719	$ 2,622,566