Investments - Schedule of investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt securities and restricted investments
Amortized Cost	$ 51,287	$ 2,531
Gross Unrealized Gains	18	11
Gross Unrealized (Losses)	(150)	(125)
Fair Value	51,155	2,417
Unrestricted available-for-sale, Debt securities
Debt securities and restricted investments
Amortized Cost	50,122	178
Gross Unrealized Gains	18
Gross Unrealized (Losses)	(143)	(125)
Fair Value	49,997	53
Unrestricted available-for-sale, Debt securities \| U.S. Treasury Bills
Debt securities and restricted investments
Amortized Cost	49,944
Gross Unrealized Gains	18
Gross Unrealized (Losses)	(14)
Fair Value	49,948
Unrestricted available-for-sale, Debt securities \| Corporate debt securities
Debt securities and restricted investments
Amortized Cost	178	178
Gross Unrealized (Losses)	(129)	(125)
Fair Value	49	53
Restricted
Debt securities and restricted investments
Amortized Cost	1,165	2,353
Gross Unrealized Gains		11
Gross Unrealized (Losses)	(7)
Fair Value	1,158	2,364
Restricted \| Short-term bond
Debt securities and restricted investments
Amortized Cost	1,165	2,239
Gross Unrealized Gains		11
Gross Unrealized (Losses)	(7)
Fair Value	$ 1,158	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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