Investments (Schedule of Available-for-sale Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 369,707	$ 59,832
Gross Unrealized Gains	7	12
Gross Unrealized Losses	(19)	(149)
Allowance for Credit Losses	(147)
Fair Value	369,548	59,695
Agency securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	39,993	1,681
Gross Unrealized Gains	2	1
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0
Fair Value	39,995	1,682
Corporate securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	197,239	49,027
Gross Unrealized Gains	4	6
Gross Unrealized Losses	(12)	(149)
Allowance for Credit Losses	(147)
Fair Value	197,084	48,884
Government securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	132,475	9,124
Gross Unrealized Gains	1	5
Gross Unrealized Losses	(7)	0
Allowance for Credit Losses	0
Fair Value	$ 132,469	$ 9,129

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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