Income taxes (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income taxes
State tax, High End		0.20%	0.20%
Reconciliation from the U.S. Federal statutory income rate of 34.0% to the effective income tax rate
Federal statutory rate	34.00%	34.00%	34.00%
State tax (less than 0.2% for 2012 and 2011)	9.20%
Permanent differences	54.30%	(4.80%)	15.10%
Foreign tax rates at rates different from U.S. rates	(82.70%)	18.80%	(48.90%)
Valuation allowance	50.20%	(51.40%)	12.00%
Total tax provision	65.00%	(3.40%)	12.20%
Uncertain tax positions	$ 0	$ 0