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Fair Value Measurement (Narrative) (Details) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2020 USD ($) broker | Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Percentage of portfolio of unadjusted fair values obtained | 98.80% |
Fair value of funds | $ 48,800,000 |
Fair Value, liability, purchases | $ 1,200,000 |
Minimum [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Number of knowledgeable outside security brokers consulted to determine fair value | broker | 1 |
Fair Value, liquidating investment, remaining period | 1 year |
Maximum [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair Value, liquidating investment, remaining period | 10 years |
Borrowings [Member] | Unsecured debt [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Unsecured notes | $ 375,000,000 | $ 375,000,000
Commercial Mortgage Back Securities [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Trading securities, fair value disclosure | 18,800,000 | 18,900,000
Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, fair value disclosure | 0 |
Liabilities, fair value | 0 |
Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, fair value disclosure | 4,162,775,000 | 4,317,826,000
Liabilities, fair value | 3,154,000 | 77,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, fair value disclosure | 3,362,326,000 | 3,156,091,000
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Borrowings [Member] | Unsecured debt [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Liabilities, fair value | 406,350,000 | 394,279,000
Fair Value, Measurements, Recurring [Member] | Borrowings [Member] | Unsecured debt [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Liabilities, fair value | $ 406,350,000 | 394,279,000
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, fair value disclosure |  | $ 1,200,000

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Estimate remaining period the underlying assets are expected to be liquidated by the investees for investments for which net asset value per share is calculated (including by unit, membership interest, or other ownership interest unit measure), in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258 + Details
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