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Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Other investments | $ 428,556 | $ 391,217
Fair value of derivative liabilities | 73,510 |
Real Estate [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Other investments | 16,150 | 16,123
Interest Rate Contract [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Other investments | 207,704 | 177,357
Illiquid Investments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Other investments | $ 85,323 | $ 84,297
Asset-backed Securities [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Inputs Coupon Rate | 5.97% | 5.97%
Fair Value Inputs Maturity | 16 years 1 month 9 days | 16 years 3 months 14 days
Fair Value Inputs Yield | 12.00% | 12.00%
Variable Interest Entity, Primary Beneficiary [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair value of derivative liabilities | $ 0 |
Variable Interest Entity, Primary Beneficiary [Member] | European Transactions [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Fair Value Inputs Coupon Rate | 2.20% | 2.20%
Fair Value Inputs Maturity | 18 years 8 months 4 days | 18 years 11 months 4 days
Fair Value Inputs Yield | 3.05% | 3.18%

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- Definition Fair value inputs coupon rate. + References No definition available. + Details
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- Definition Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226006-175313 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 + Details
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