Summary of Investments (Unrealized Appreciation) (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Change in net unrealized investment appreciation
Available-for-sale fixed maturities	$ (65,127)	$ 32,132
Available-for-sale equity securities	0	11,861
Deferred policy acquisition costs	7,274	(3,753)
Income tax effect	12,148	(14,084)
Net unrealized investment depreciation of discontinued operations, sold	6,714	0
Cumulative change in accounting principles			$ (191,244)	$ 0
Total change in net unrealized investment appreciation, net of tax	$ (230,235)	$ 26,156

Equity Securities, Change in Net Unrealized Holding Gain (Loss), Before Tax

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Other Comprehensive Income (Loss), Available-For-Sale Securities Adjustment, Securities Sold, Net Of Tax, Portion Attributable To Parent

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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

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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, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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