Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities, Interest Income	$ 0	$ 110
Amortized Cost	25,712,000	22,618,000
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	1,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	25,712,000	22,619,000
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,864,000	9,374,000
Fair Value	3,864,000	9,375,000
Money market mutual funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,848,000	13,244,000
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	21,848,000	13,244,000
United States treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,002,000
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0
Fair Value		1,002,000
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,283,000
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0
Fair Value		2,284,000
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,864,000	6,089,000
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	$ 3,864,000	$ 6,089,000