Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) - Successor [Member] - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2017

Sep. 30, 2016

Mar. 31, 2016

Sep. 30, 2017

Sep. 30, 2016

Dec. 31, 2016

Jun. 30, 2017

Jun. 30, 2016

Dec. 31, 2015

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Available-for-sale Securities

$ 5,794,058

$ 6,049,908

Ambac insured Re-remic [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Coupon rate

1.74%

Fair Value Inputs Maturity

10 months 10 days

Yield

0.00%

Variable Interest Entity, Primary Beneficiary [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

$ 323,192

$ 1,226,106

Variable Interest Entity, Primary Beneficiary [Member] | United States Transactions [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Coupon rate

5.88%

Fair Value Inputs Maturity

23 days

20 years 8 months 68 days

Yield

5.88%

5.86%

Fair Value, Inputs, Level 3 [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

$ 12,232,247

$ 12,363,248

$ 12,232,247

12,363,248

$ 11,369,112

$ 12,044,498

$ 12,021,381

$ 11,497,098

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

66,569

622,065

410,104

1,244,712

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss

332,207

(216,229)

934,431

(1,326,847)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases

7,126

35,781

99,018

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales

79,319

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

211,027

71,095

459,940

10,571

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

22,078

100,798

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

737,898

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

58,097

606,031

327,787

1,201,113

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

684,638

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

26,033

Fair Value, Inputs, Level 3 [Member] | Ambac insured Re-remic [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Available-for-sale Securities

Fair Value, Inputs, Level 3 [Member] | Corporate Obligations [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Available-for-sale Securities

Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Corporate Obligations [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

2,588,556

Available-for-sale Securities

2,785,608

2,622,566

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

571,739

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss

(331,610)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

571,739

Derivative [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

53,089

(119,106)

$ (104,032)

53,089

(119,106)

(100,282)

52,729

(99,192)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

2,031

(12,220)

53,329

(23,250)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

1,671

2,854

(100,042)

3,336

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

1,889

(12,450)

5,640

(24,026)

Derivative [Member] | Interest Rate Swap [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

62,050

(84,933)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

45,474

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

(101,509)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

5,715

Derivative [Member] | Credit Derivative [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

(8,961)

$ (15,349)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

7,855

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

1,467

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

(75)

Credit Derivative [Member] | Derivative [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

(16,700)

(34,543)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

18,554

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

(711)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

17,778

Credit Derivative [Member] | Derivative [Member] | Credit Derivative [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

(8,961)

(16,700)

(18,207)

(8,961)

(16,700)

(9,006)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

179

1,733

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

134

226

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

1,503

Interest Rate Swap [Member] | Derivative [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

(102,406)

$ (64,649)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

(41,804)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

4,047

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

(41,804)

Interest Rate Swap [Member] | Derivative [Member] | Interest Rate Swap [Member]

Fair Value Inputs, Assets, Quantitative Information [Line Items]

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability

62,050

(102,406)

(85,825)

$ 62,050

$ (102,406)

$ 61,735

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings

1,852

(13,953)

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements

1,537

2,628

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three

$ 0

Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held

$ 1,852

$ (13,953)