Investments and Fair Value Measurements - Schedule of Available for Sale Securities Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Cost	$ 4,572,000	$ 11,592,000
Unrealized Gain	1,000
Unrealized Loss	(48,000)	(113,000)
Fair Value	4,525,000	11,479,000
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	393,000	1,202,000
Unrealized Gain	1,000
Unrealized Loss		(1,000)
Fair Value	394,000	1,201,000
Short-term Investments [Member] | U.S. Treasury Notes [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	302,000	1,066,000
Unrealized Gain	1,000
Unrealized Loss		(1,000)
Fair Value	303,000	1,065,000
Short-term Investments [Member] | Corporate Bonds and Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	91,000	136,000
Unrealized Gain
Unrealized Loss
Fair Value	91,000	136,000
Long-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	4,179,000	10,390,000
Unrealized Gain
Unrealized Loss	(48,000)	(112,000)
Fair Value	4,131,000	10,278,000
Long-term Investments [Member] | U.S. Treasury Notes [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	1,569,000	3,367,000
Unrealized Gain
Unrealized Loss	(2,000)	(37,000)
Fair Value	1,567,000	3,330,000
Long-term Investments [Member] | Corporate Bonds and Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	1,062,000	2,744,000
Unrealized Gain
Unrealized Loss	(23,000)	(35,000)
Fair Value	1,039,000	2,709,000
Long-term Investments [Member] | Government Agency Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	1,548,000	4,279,000
Unrealized Gain
Unrealized Loss	(23,000)	(40,000)
Fair Value	$ 1,525,000	$ 4,239,000