2. Summary of significant accounting policies (Details) - Product Warranty Liability (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Product Warranty Liability [Abstract]
Balance, beginning of period	$ 274	$ 421	$ 249
Warranties issued	492	104	472
Acquisition of business			25
Warranty settlements	(400)	(251)	(325)
Balance, end of period	$ 366	$ 274	$ 421