Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(13))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(14))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(8))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Name:	us-gaap_PropertyPlantAndEquipmentNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Business Segments, Concentration of Credit Risk and Significant Customers - Significant Customers (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016 USD ($) customer	Dec. 31, 2015
Significant Customers
Property and equipment, net	$ 827	$ 1,274
United States
Significant Customers
Property and equipment, net	$ 827	$ 1,274
Customer A
Significant Customers
Percentage of concentration risk	46.00%
Customer B
Significant Customers
Percentage of concentration risk	17.00%	21.00%	12.00%
Customer C
Significant Customers
Percentage of concentration risk	11.00%	47.00%	34.00%
Customer D
Significant Customers
Percentage of concentration risk		13.00%	31.00%
Net accounts receivable \| Credit concentration \| One customer
Significant Customers
Percentage of concentration risk	63.00%	72.00%
Number of customers \| customer	1	1