Investments - Net Realized Investment Gains (Losses) Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings	$ 751	$ 490	$ 12,952
Portion of OTTI losses recognized in other comprehensive income before taxes	227	0	248
Investment Tax Credit Carryforward \| Investment in unconsolidated subsidiaries
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings			3,400
Corporate debt
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings	800	$ 500	200
Portion of OTTI losses recognized in other comprehensive income before taxes	$ 227		248
Early Stage Business Development \| Investment in unconsolidated subsidiaries
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings			$ 8,500

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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