Concentration of Risk (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Accounts receivable | Concentration of credit risk
Concentration of risks
Number of largest individual trade receivable balances	2	2
Accounts receivable | Concentration of credit risk | Customer with largest individual trade balance
Concentration of risks
Concentration risk, percentage	28.00%	55.00%
Accounts receivable | Concentration of credit risk | Customer with second largest individual trade balance
Concentration of risks
Concentration risk, percentage	18.00%	25.00%
U.S. workforce | Labor concentration risk
Concentration of risks
Concentration risk, percentage	72.00%