Summary of significant accounting policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Reclassification of Other operating expenses to Compensation and benefits		$ 74,000
Cash equivalents	$ 6,301,000	$ 7,833,000
Weighted average number of common shares outstanding	19,085,000	19,250,000
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding	132,000	204,000
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding	3,350,000	3,250,000