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Investments - Summary of Net Investment Income (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Investment [Line Items] |  |
Net Realized and Unrealized Gain (Loss) on Trading Securities | $ 6,947 | $ (1,579)
Trading Securities, Realized Gain (Loss) | 631 | 1,933
Investment expense | (1,411) | (1,827)
Securities available-for-sale and short-term | 46,552 | 110,551
Total net investment income | 54,842 | 110,240
Gains (losses) on securities held as of reporting date [Member] |  |
Investment [Line Items] |  |
Other Investments Income | 6,316 | (3,512)
Fixed Income Investments [Member] |  |
Investment [Line Items] |  |
Gross Investment Income, Operating | 43,666 | 109,351
Short-Term [Member] |  |
Investment [Line Items] |  |
Gross Investment Income, Operating | 4,113 | 2,840
Loans Receivable [Member] |  |
Investment [Line Items] |  |
Gross Investment Income, Operating | 184 | 187
Other Investments [Member] |  |
Investment [Line Items] |  |
Gross Investment Income, Operating | $ 8,290 | $ (311)

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- Definition Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 + Details
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