Investments -Summary of Aggregate Fair Value and Gross Unrealized Loss by Length of Time (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value
Less Than 12 Months	$ 0	$ 0
12 Months or Longer	1,283	1,302
Total	1,283	1,302
Unrealized Loss
Less Than 12 Months	0	0
12 Months or Longer	(23)	(26)
Total	(23)	(26)
Municipal bonds
Fair Value
Less Than 12 Months	0	0
12 Months or Longer	1,283	1,302
Total	1,283	1,302
Unrealized Loss
Less Than 12 Months	0	0
12 Months or Longer	(23)	(26)
Total	$ (23)	$ (26)