Investments - Summary of Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended
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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Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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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

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 944
-SubTopic 220
-Section S99
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Amount, after 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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
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