Investments (Details 3) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Debt securities, held-to-maturity	$ 56,233,000
Short-term Investments [Member] | Available For Sale[Member]
Debt securities, held-to-maturity	561,000	$ 1,052,000
Gross Unrealized Fair Value	462,000	1,105,000
Gross Unrealized Gains		53,000
Gross Unrealized Losses	(99,000)
Short-term Investments [Member] | Mutual Funds [Available For Sale] [Member]
Debt securities, held-to-maturity	5,675,000	5,675,000
Gross Unrealized Fair Value	2,123,000	2,822,000
Gross Unrealized Losses	(3,552,000)	(2,853,000)
Money Market Funds [Member] | Short-term Investments [Member]
Debt securities, held-to-maturity	1,861,000	3,460,000
Gross Unrealized Fair Value	1,861,000	3,460,000
Commercial Paper [Member] | Short-term Investments [Member]
Debt securities, held-to-maturity	5,459,000	9,424,000
Gross Unrealized Fair Value	5,473,000	9,426,000
Gross Unrealized Gains	14,000	2
Bonds [Member] | Short-term Investments [Member]
Debt securities, held-to-maturity	56,233,000	44,833,000
Gross Unrealized Fair Value	56,763,000	44,952,000
Gross Unrealized Gains	575,000	138,000
Gross Unrealized Losses	$ (45,000)	$ (19,000)