Investments (Narrative) (Details) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2019 USD ($) securities	Dec. 31, 2018 USD ($) securities
Schedule of Investments [Line Items]
Available-for-sale fixed maturity securities in unrealized loss position, number of positions \| securities	304	1,005
Available-for-sale securities, estimated fair value	$ 1,129,104	$ 4,594,664
Available-for-sale securities, gross unrealized holding losses	$ (16,908)	$ (133,989)
Number of available-for-sale fixed maturity securities positions in a continuous unrealized loss position for one year or longer at period end \| securities	267	541
Investment Maturity Period	1 year	1 year
Available-for-sale securities, estimated fair value, 12 months or longer	$ 973,892	$ 1,983,912
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(12,307)	(77,504)
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	1,110,282	4,397,021
Available-for-sale securities, gross unrealized holding losses	(16,527)	(131,215)
Available-for-sale securities, estimated fair value, 12 months or longer	972,115	1,983,912
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	$ (12,242)	$ (77,504)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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