Investments - Net Realized Gains (Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary impairment losses on securities	$ (1,530)	$ (12,620)	$ (11,401)
Portion of losses recognized in other comprehensive income (loss)	0	0	(290)
Net other-than-temporary impairment losses on securities recognized in earnings	(1,530)	(12,620)	(11,111)
Sales and other, net	3,491	7,756	16,286
Change in fair value - equity securities	(18,323)	0	0
Change in fair value and gains realized on settlements - derivative instruments	3,819	1,458	(1,052)
Total	$ (12,543)	$ (3,406)	$ 4,123

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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The amount by which the fair value of an investment 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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Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

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Amount before tax of other than temporary impairment (OTTI) loss on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss.

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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