General - Investments - Amortized Cost (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized cost
Amortized Cost	$ 630,519	$ 143,561
Gross Unrealized Gains	43	14
Gross Unrealized Losses	(132)	(116)
Estimated Fair Value	630,430	143,459
U.S. Government and agency securities
Amortized cost
Amortized Cost	332,375	42,389
Gross Unrealized Gains	29	11
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	332,403	42,399
Corporate debt securities
Amortized cost
Amortized Cost	296,833	99,861
Gross Unrealized Gains	14	3
Gross Unrealized Losses	(131)	(115)
Estimated Fair Value	296,716	99,749
Certificates of deposit
Amortized cost
Amortized Cost	1,311	1,311
Estimated Fair Value	$ 1,311	$ 1,311

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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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Amount of 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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