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Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Detail) - Successor [Member] - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | $ 186,304 | $ 30,775 | $ 252,687 | $ 39,861
Net Change in Fair Value of Credit Derivatives [Member] | Credit Derivatives [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | (217) | 6,624 | (563) | 7,676
Derivative Products [Member] | Interest Rate Swap [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | 1,620 | 37,141 | 6,163 | 37,249
Derivative Products [Member] | Futures Contracts [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | 7,529 | (3,073) |  |
Derivative Products [Member] | Other Contracts [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total |  |  | 28,523 | (4,695)
Derivative Products [Member] | ERROR in label resolution. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | 9,149 | 34,068 | 34,686 | 32,554
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | 177,372 | (9,917) | 218,564 | (369)
Income Loss On Variable Interest Entities [Member] | Interest Rate Swap [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | 163,229 | 34 | 213,038 | 14,530
Income Loss On Variable Interest Entities [Member] | Currency Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net, Total | $ 14,143 | $ (9,951) | $ 5,526 | $ (14,899)

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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