Sale-leaseback transaction (Details)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	14 Months Ended
	Mar. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Mar. 31, 2014 tranche	Dec. 31, 2014 USD ($)
Sale-leaseback transaction
Proceeds from sale of assets	$ 795,000					$ 5,500,000
Number of tranches | tranche							5
Deferred gain						$ 2,700,000		$ 116,000
Lease term				42 months
Net gain on sale leaseback transaction		$ 208,000	$ 208,000	$ 416,000	$ 408,000