Property and equipment (Narrative) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Property And Equipment Narrative Details
Property and equipment under capital lease	$ 704,000	$ 704,000
Accumulated depreciation related to assets under capital lease	$ 704,000	$ 704,000

The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 2)
-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant