Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant and Equipment Estimated Useful Lives

Property, plant and equipment are amortized over their estimated useful lives using the straight-line method based on the following rates:

Asset	Rate
Research equipment	5 years
Office furniture and equipment	5 years
Computer equipment	3 years
Leasehold improvements	Over the lesser of lease term or estimated useful life

Collaboration Research And Development Revenue [Member]

Revenue Recognized From Collaborations

Collaborators whose collaboration research and development revenue accounted for 10% or more of total revenues were as follows

	Year ended December 31,
	2017		2016		2015
Genentech	$	250	$	1,651	$	4,563
Teva		59		116		11,010