Income taxes (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross balance at January 1	$ 50	$ 213
Additions based on tax positions related to the current year	0	0
Additions for tax positions of prior years	0	16
Reductions for tax positions of prior years	0	0
Settlements	0	(179)
Reductions due to lapse of applicable statute of limitations	0	0
Gross balance at December 31	50	50
Interest and penalties	22	22
Balance including interest and penalties at December 31	$ 72	$ 72