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Fair Value Measurements - Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings (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
Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period |  |  | $ (71,072) | $ 266,629
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held |  |  | (71,072) | 266,629
Net Investment Income [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period | $ 282 | $ 16,479 | 35,466 |
Total gains or losses included in earnings for the period |  |  |  | 26,298
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | 0 | 0 | 0 | 0
Realized Gains Or (Losses) and Other Settlements On Credit Derivative Contracts [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period | 91 | 1,134 | 197 | 1,333
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | 0 | 0 | 0 | 0
Unrealized Gains Or (Losses) On Credit Derivative Contracts [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period | (308) | 5,490 | (760) | 6,343
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | (308) | 191 | (760) | 51
Interest Rate Swap [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period | (2,465) | 47,491 | (11,494) | 43,622
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | (2,465) | 4,049 | (11,494) | 3,863
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period | 40,557 | 20,039 |  |
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | 40,557 | 20,039 |  |
Other Income or (Loss) [Member] |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Total gains or losses included in earnings for the period | (366) | (348) | (724) | (691)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held | $ (366) | $ (348) | $ (724) | $ (691)

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- Definition The amount of gains or losses included in earnings attributable to unrealized gains or losses on financial instruments measured on a recurring basis using unobservable inputs that are still held at the reporting date. + References No definition available. + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets); the fair value of which assets and liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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