Commitments and Contingencies - Operating Leases Narrative (Details) - USD ($) $ in Thousands					12 Months Ended
	Dec. 01, 2016	Jan. 07, 2015	Mar. 20, 2014	Sep. 09, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leased Assets [Line Items]
Minimum lease payments					$ 459
Future minimum sublease payments					127
Rent expense					754	$ 782	$ 667
Deferred rent payable					36	69
Rental income					350	$ 349	$ 132
New York | Office space
Operating Leased Assets [Line Items]
Term of lease (in years)				5 years
Initial annual rent				$ 139
Monthly rent installment				$ 12
Minimum lease payments					115
Security deposit					$ 69
Percentage of annual rent increase					2.50%
Future minimum sublease payments					$ 127
Menlo Park, California | Office space
Operating Leased Assets [Line Items]
Monthly rent installment			$ 165
East Palo Alto, California | Office space
Operating Leased Assets [Line Items]
Initial annual rent		$ 450
Minimum lease payments					$ 344
Security deposit		$ 231
Percentage of annual rent increase		3.00%
Tel Aviv, Israel
Operating Leased Assets [Line Items]
Initial annual rent	$ 12