Field Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Field Equipment [Line Items]
Depreciation	$ 1,968	$ 1,673	$ 1,348
Impairment of field equipment		6,412
Field equipment
Field Equipment [Line Items]
Depreciation	4,483	3,248	1,555
Field Equipment Under Operating Leases
Field Equipment [Line Items]
Impairment of field equipment	$ 195	6,436	$ 36
First Generation Optune System Field Equipment | Cost of Revenues
Field Equipment [Line Items]
Impairment of field equipment		6,412
First Generation Optune System Field Equipment | Cost of Revenues | Finished Goods
Field Equipment [Line Items]
Impairment of field equipment		4,830
First Generation Optune System Field Equipment | Cost of Revenues | Production Stage Goods
Field Equipment [Line Items]
Impairment of field equipment		$ 1,582