Investments - Schedule of investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt securities and restricted investments
Amortized Cost	$ 18,422
Gross Unrealized Gain	28
Gross Unrealized Loss	842
Fair Value	17,608
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	15,003
Gross Unrealized Gain	28
Gross Unrealized Loss	829
Fair Value	14,202
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	9,961
Gross Unrealized Loss	15
Fair Value	9,946
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	5,042
Gross Unrealized Gain	28
Gross Unrealized Loss	814
Fair Value	4,256
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	3,419
Gross Unrealized Loss	13
Fair Value	3,406
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	3,252
Gross Unrealized Loss	13
Fair Value	3,239
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 investments in debt securities classified as available-for-sale.

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