Investments, Net Realized and Unrealized Gains (Losses) on Investments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Components of net realized and unrealized gains (losses) on investments [Abstract]
Gross gains on available-for-sale fixed income securities sold during the period	$ 3,171	$ 2,443
Gross losses on available-for-sale fixed income securities sold during the period	(3,527)	(2,708)
Other-than-temporary impairments	(260)	0
Change in value of limited partnership investments	408	(2,603)
Gains (losses) on equity securities [Abstract]
Realized gains on equity securities sold during the period	317	641
Unrealized gains (losses) on equity securities held at the end of the period	5,919	(2,306)
Realized and unrealized gains (losses) on equity securities during the period	6,236	(1,665)
Net realized and unrealized gains (losses) on investments	6,028	$ (4,533)
Federal income taxes	$ 27,203

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Amount of realized gain (loss) from a change in the value of investments in limited partnerships.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading 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 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 of current and deferred federal income tax expense (benefit) attributable to income (loss) from continuing operations.

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Amount of realized and unrealized gain (loss) on investment.

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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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