Investments - Aggregate Fair Value and Gross Unrealized Loss in Continuous Unrealized Loss Position (Details)	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security	Sep. 30, 2019 USD ($)
Fair Value
Less Than 12 Months	$ 2,152,000	$ 3,387,000
12 Months or Longer	0	0
Total	2,152,000	3,387,000
Unrealized Loss
Less Than 12 Months	(3,000)	(8,000)
12 Months or Longer	0	0
Total	(3,000)	(8,000)
Credit losses recognized in earnings	0		$ 0
Available-for-sale securities	$ 13,296,000	$ 9,306,000
Number of securities in unrealized loss position for less than 12 months | security	4	5
Number of securities in unrealized loss position for more than 12 months | security	0	0
Treasury bills
Fair Value
Less Than 12 Months	$ 1,033,000
12 Months or Longer	0
Total	1,033,000
Unrealized Loss
Less Than 12 Months	0
12 Months or Longer	0
Total	$ 0
Number of portfolio securities | security	3
Available-for-sale securities	$ 1,976,000
Municipal bonds
Fair Value
Less Than 12 Months	909,000	$ 3,387,000
12 Months or Longer	0	0
Total	909,000	3,387,000
Unrealized Loss
Less Than 12 Months	(2,000)	(8,000)
12 Months or Longer	0	0
Total	$ (2,000)	$ (8,000)
Number of portfolio securities | security	10	8
Available-for-sale securities	$ 5,254,000	$ 3,370,000
Agency mortgage-backed securities
Fair Value
Less Than 12 Months	210,000
12 Months or Longer	0
Total	210,000
Unrealized Loss
Less Than 12 Months	(1,000)
12 Months or Longer	0
Total	$ (1,000)
Number of portfolio securities | security	16	13
Available-for-sale securities	$ 6,066,000	$ 5,936,000