Investments - Schedule of Investments' Gross Unrealized Loss and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 6,432	$ 6,323
Unrealized Losses, Less than 12 Months	(42)	(6)
Fair Value, 12 Months or More	2,246	12,734
Unrealized Losses, 12 Months or More	(5)	(216)
Fair Value	8,678	19,057
Unrealized Losses	(47)	(222)
U.S. Treasury securities, obligations of U.S. Government agencies and Municipalities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	5,435	5,866
Unrealized Losses, Less than 12 Months	(32)	(6)
Fair Value, 12 Months or More	2,246	12,634
Unrealized Losses, 12 Months or More	(5)	(216)
Fair Value	7,681	18,500
Unrealized Losses	(37)	(222)
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	997	457
Unrealized Losses, Less than 12 Months	(10)	0
Fair Value, 12 Months or More	0	100
Unrealized Losses, 12 Months or More	0	0
Fair Value	997	557
Unrealized Losses	$ (10)	$ 0