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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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	$ 3,867,547		$ 3,867,547		$ 5,309,161
Ambac insured Re-remic [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate					2.05%
Fair Value Inputs Maturity					19 days
Yield					10.00%
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			(113,996)	$ 323,192
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	7,169,406	$ 12,232,247	7,169,406	12,232,247	$ 12,561,185	$ 11,369,112	$ 11,110,155	$ 12,044,498
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies					3,709,113	3,709,113
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(36,221)	66,569	(84,608)	410,104
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	(122,362)	332,207	(435,776)	934,431
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	35,781
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	(79,319)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	73,053	211,027	1,156,973	(459,940)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three			0	22,078
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three			5,309	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	(36,696)	58,097	(129,521)	327,787
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					709,950
Fair Value, Inputs, Level 3 [Member] | Ambac insured Re-remic [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities					26,067
Fair Value, Inputs, Level 3 [Member] | Corporate Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	0		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]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability						2,622,566
Available-for-sale Securities	2,718,377		2,718,377		2,914,145
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				(49,518)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				228,487
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(15,927)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three				0
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				(49,518)
Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	42,237	53,089	42,237	53,089	60,808	(100,282)	45,613	52,729
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(2,080)	2,031	(14,137)	53,329
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	1,296	1,671	4,434	100,042
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three	0	0	0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	(2,179)	1,889	(14,433)	5,640
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	43,412		43,412		61,374
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(13,824)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			4,138
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three			0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(13,824)
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	(1,175)		(1,175)		$ (566)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(313)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			296
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three			0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(609)
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		(8,961)		(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 Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
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				0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				(75)
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	(1,175)	(8,961)	(1,175)	(8,961)			(1,326)	(9,006)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	250	179
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	99	134
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three	0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	151	37
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		62,050		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 Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
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				0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				5,715
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	43,412	62,050	$ 43,412	$ 62,050			$ 46,939	$ 61,735
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(2,330)	1,852
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	1,197	1,537
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three	0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	$ (2,330)	$ 1,852

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Fair value of financial instruments measured on a recurring basis using unobservable inputs removed as a result of the deconsolidation of variable interest entities.

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Amount of gain or loss included in earnings arising from financial instruments measured on a recurring basis using unobservable inputs.

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Amount of gain or loss included in other comprehensive income arising from financial instruments measured on a recurring basis using unobservable inputs.

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Amount of purchases of financial instruments measured on a recurring basis using unobservable inputs.

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Amount of settlements related to financial instruments measured on a recurring basis using unobservable inputs.

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Amount of change in fair value of financial instruments measured on a recurring basis using unobservable inputs arising from transfers into level 3 of the fair value hierarchy.

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Amount of change in fair value of financial instruments measured on a recurring basis using unobservable inputs arising from transfers out of level 3 of the fair value hierarchy.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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