Investments - Schedule of investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt securities and restricted investments
Amortized Cost	$ 13,285
Gross Unrealized Gain	1
Gross Unrealized Loss	(896)
Fair Value	12,390
Debt securities, equity securities and restricted investments
Amortized Cost		$ 118,110
Gross Unrealized Gains		834
Gross Unrealized Losses		(3,207)
Fair Value		115,737
Unrestricted available-for-sale, Debt securities
Debt securities and restricted investments
Amortized Cost	9,844
Gross Unrealized Gain	1
Gross Unrealized Loss	(887)
Fair Value	8,958
Debt securities, equity securities and restricted investments
Amortized Cost		77,673
Gross Unrealized Gains		411
Gross Unrealized Losses		(1,839)
Fair Value		76,245
Unrestricted available-for-sale, Debt securities \| U.S. Treasury securities
Debt securities and restricted investments
Amortized Cost	6,936
Gross Unrealized Gain	1
Fair Value	6,937
Debt securities, equity securities and restricted investments
Amortized Cost		9,892
Gross Unrealized Losses		(22)
Fair Value		9,870
Unrestricted available-for-sale, Debt securities \| Corporate debt securities
Debt securities and restricted investments
Amortized Cost	2,908
Gross Unrealized Loss	(887)
Fair Value	2,021
Debt securities, equity securities and restricted investments
Amortized Cost		67,781
Gross Unrealized Gains		411
Gross Unrealized Losses		(1,817)
Fair Value		66,375
Equity securities \| Preferred stock
Debt securities, equity securities and restricted investments
Amortized Cost		35,955
Gross Unrealized Gains		423
Gross Unrealized Losses		(1,355)
Fair Value		35,023
Restricted
Debt securities and restricted investments
Amortized Cost	3,441
Gross Unrealized Loss	(9)
Fair Value	3,432
Debt securities, equity securities and restricted investments
Amortized Cost		4,482
Gross Unrealized Losses		(13)
Fair Value		4,469
Restricted \| Short-term bond
Debt securities and restricted investments
Amortized Cost	3,274
Gross Unrealized Loss	(9)
Fair Value	3,265
Debt securities, equity securities and restricted investments
Amortized Cost		4,264
Gross Unrealized Losses		(13)
Fair Value		4,251
Restricted \| Money market fund
Debt securities and restricted investments
Amortized Cost	167
Fair Value	$ 167
Debt securities, equity securities and restricted investments
Amortized Cost		218
Fair Value		$ 218

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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