Investments - Schedule of investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt securities and restricted investments
Amortized Cost	$ 17,004
Gross Unrealized Gain	4
Gross Unrealized Loss	402
Fair Value	16,606
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	13,562
Gross Unrealized Gain	4
Gross Unrealized Loss	389
Fair Value	13,177
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	9,996
Gross Unrealized Loss	2
Fair Value	9,994
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	3,566
Gross Unrealized Gain	4
Gross Unrealized Loss	387
Fair Value	3,183
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	3,442
Gross Unrealized Loss	13
Fair Value	3,429
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	3,275
Gross Unrealized Loss	13
Fair Value	3,262
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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-Section 50
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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 and equity securities categorized neither as held-to-maturity nor trading.

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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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