Share-based compensation (Details Textual) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation expense	$ 346	$ 197	$ 1,208	$ 229
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	831	1,281	831	1,281
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term			8 months 12 days
Class of Warrant or Right, Exercise Price of Warrants or Rights	3.85		3.85		4
Warrants Expiry Description			all issued warrants are exercisable and expire through 2017
Share Based Compensation Arrangement By Share Based Payment Award Warrants Exercised			715,742
Maximum Number of warrants allowed			1,431,486
Exchange of warrant into common stock			894,683
Proceeds from Warrant Exercises			3,047	0
Common stock purchase warrant exercised	307,204		307,204
Common stock purchase warrant exercise price			$ 3.00
Conversion of warrants to cashless shares			210,529
Conversion of warrants exercised			96,675
Conversion Of Warrants To Common Stock Value			290
Noncontrolling Interest [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation expense	$ 0		$ 15