Commitments and contingencies (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies [Line Items]
Estimated Litigation Liability	$ 6,200,000
Litigation Settlement, Expense	$ 275,000
Interest Rate Description Litigation	plus legal interest that accrued at 12% per annum from August 13, 2008 to June 30, 2013, and thereafter accrued and continues to accrue at 6% per annum.
Operating Leases, Rent Expense	$ 2,300,000	$ 2,700,000

Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.25)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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