Concentration of Risk (Details)	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended		3 Months Ended
	Mar. 31, 2013 Consolidated accounts receivable Credit concentration risk item	Dec. 31, 2012 Consolidated accounts receivable Credit concentration risk item	Mar. 31, 2013 Consolidated accounts receivable Credit concentration risk One customer	Dec. 31, 2012 Consolidated accounts receivable Credit concentration risk One customer	Dec. 31, 2012 Consolidated accounts receivable Credit concentration risk Second customer	Mar. 31, 2013 Consolidated Revenue Customer concentration risk item	Mar. 31, 2012 Consolidated Revenue Customer concentration risk item	Mar. 31, 2013 Consolidated Revenue Customer concentration risk One customer	Mar. 31, 2012 Consolidated Revenue Customer concentration risk One customer	Mar. 31, 2012 Consolidated Revenue Customer concentration risk Second customer
Concentration of risk
Number of customers	1	2				1	2
Percentage of concentration risk			12.90%	11.90%	11.50%			11.50%	24.60%	14.40%