Income taxes, Income Tax Contingency (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Contingency [Line Items]
Accrued interest and penalties related to unrecognized tax benefits	$ 25,000	$ 26,000
Unrecognized tax benefits, current	153,000	104,000
Unrecognized tax benefits, noncurrent	863,000	952,000
Estimated unrecognized tax benefits expected to be reversed within next twelve months	75,000	50,000
Gross unrecognized tax benefits activity [Roll Forward]
Gross unrecognized tax benefits, beginning balance	1,056,000	950,000	260,000
Increases for tax positions for prior years	25,000	167,000	16,000
Decreases for tax positions for prior years	(65,000)	(61,000)	(175,000)
Increases for tax positions for current year	0	0	849,000
Settlements	0	0	0
Lapse of statue of limitations	0	0	0
Gross unrecognized tax benefits, ending balance	$ 1,016,000	$ 1,056,000	$ 950,000