Restricted Investments (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2018 USD ($) Securities	Dec. 31, 2017 USD ($) Securities
Schedule of Investments [Line Items]
Cost or Amortized Cost	[1]	$ 22,281	$ 22,232
Gross Unrealized Gains		0	0
Gross Unrealized Temporary Losses		(39)	(24)
Estimated Fair Value	[1]	$ 22,242	$ 22,208
Securities with unrealized losses for less than 12 months | Securities		38	32
Impairment losses		$ 0
United States corporate securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost		15,982	$ 15,982
Gross Unrealized Gains		0	0
Gross Unrealized Temporary Losses		(32)	(14)
Estimated Fair Value		15,950	15,968
Municipal bonds [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost		5,019	4,970
Gross Unrealized Gains		0	0
Gross Unrealized Temporary Losses		(7)	(10)
Estimated Fair Value		5,012	4,960
Negotiable certificate of deposits [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost		1,280	1,280
Gross Unrealized Gains		0	0
Gross Unrealized Temporary Losses		0	0
Estimated Fair Value		$ 1,280	$ 1,280
Maximum [Member]
Schedule of Investments [Line Items]
Contractual maturities of fixed maturity securities		1 year
Duration of securities in unrealized loss position		12 months

[1] Restricted investments are included in "Restricted investments, held to maturity, amortized cost."