Investments - Schedule of investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt securities and restricted investments
Amortized Cost	$ 51,203	$ 2,531
Gross Unrealized Gains	14	11
Gross Unrealized (Losses)	(2)	(125)
Fair Value	51,215	2,417
Unrestricted available-for-sale, Debt securities
Debt securities and restricted investments
Amortized Cost	50,033	178
Gross Unrealized Gains	4
Gross Unrealized (Losses)	(2)	(125)
Fair Value	50,035	53
Unrestricted available-for-sale, Debt securities \| U.S. Treasury Bills
Debt securities and restricted investments
Amortized Cost	49,973
Gross Unrealized Gains	4
Gross Unrealized (Losses)	(2)
Fair Value	49,975
Unrestricted available-for-sale, Debt securities \| Corporate debt securities
Debt securities and restricted investments
Amortized Cost	60	178
Gross Unrealized (Losses)		(125)
Fair Value	60	53
Restricted
Debt securities and restricted investments
Amortized Cost	1,170	2,353
Gross Unrealized Gains	10	11
Fair Value	1,180	2,364
Restricted \| Short-term bond
Debt securities and restricted investments
Amortized Cost	1,170	2,239
Gross Unrealized Gains	10	11
Fair Value	$ 1,180	2,250
Restricted \| Money market fund
Debt securities and restricted investments
Amortized Cost		114
Fair Value		$ 114

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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