Investments - Net Investment Gains (Losses) By Transaction Type (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Credit impairment write-downs	$ 0	$ 0	$ 0	$ 0
Change in intent write-downs	(523)	(34)	(4,215)	(271)
Net other-than-temporary impairment losses on securities recognized in earnings	(523)	(34)	(4,215)	(271)
Sales and other, net	352	142,067	4,909	146,905
Change in fair value - equity securities	6,600	3,441	(7,886)	6,948
Change in fair value and gains (losses) realized on settlements - derivatives	(3,267)	859	(8,110)	168
Net investment gains (losses)	$ 3,162	$ 146,333	$ (15,302)	$ 153,750

Other than Temporary Impairment Losses, Investments, Portion Recognized In Earnings, Change In Intent

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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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).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings.

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Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

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Amount of realized gain (loss) on investment.

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