Impact of recent accounting standards (Details Textual)	9 Months Ended
Sep. 30, 2018
Accounting Standards Update 2016-15 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Description of Prior-period Information Retrospectively Adjusted	the adoption resulted in a reclassification of approximately $1.1 million in cash inflows related to the distribution of earnings from OC-BVI from investing activities to operating activities

Description of the prior-period information that has been retrospectively adjusted when a new accounting pronouncement or a change in accounting principle is adopted.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration