Investment in Securities - Change in Net Unrealized Gains (Losses) on Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Adjustments for
Deferred policy acquisition costs	$ 38,893
Change in net unrealized gains (losses) on debt securities, net of tax	85,514	$ (91,333)
Unrealized gains (losses) on equity securities
Net gains (losses) on equity securities	206,377	(33,170)
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Bonds available-for-sale: change in unrealized gains (losses)	154,167	(143,168)
Adjustments for
Deferred policy acquisition costs	(38,893)	20,054
Participating policyholders’ interest	(7,690)	6,953
Deferred federal income tax benefit (expense)	(22,070)	24,828
Change in net unrealized gains (losses) on debt securities, net of tax	85,514	(91,333)
Equity Securities
Unrealized gains (losses) on equity securities
Unrealized gains (losses) on equity securities	203,022	(34,225)
Net gains on equity securities sold	3,355	1,055
Net gains (losses) on equity securities	$ 206,377	$ (33,170)

Change in unrealized (gains) losses of investments attributable to participating policyholders' interest.

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Net Unrealized Gains Losses On Debt Securities Adjustment [Abstract]

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Amount of unrealized investment gain (loss) which decreases (increases) deferred policy acquisition cost.

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-Topic 321
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-Section 50
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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Line items represent financial 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.

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